Name: preparation of homogeneous maldi samples for quantitative applications
Uploaded: 2016-10-28T13:00:00
Description: Watch this Scientific Journal Video about Preparation of Homogeneous MALDI Samples for Quantitative Applications at JoVE.com

This work is supported by the Genomics Research Center, Academia Sinica and the Ministry of Science and Technology of Taiwan, the Republic of China (Contract No. 104-2119-M-001-014).

NOTE: This protocol is developed for reducing the spatial heterogeneity of maltotriose and bradykinin fragment (1-7) prepared with the dried-droplet method. The protocol consists of three main steps, including preparation and preconditioning, sample deposition and drying, and mass spectrometry data analysis. The procedures are outlined and described in more detail below:
1. Preparation and Preconditioning
<ol>
	<li>Cleaning the Sample Plate
	<ol>
		<li>Wear nitrile gloves and hand-wash the sample plate gently wi...

<ol>
	<li>Karas, M., Hillenkamp, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser+Desorption+Ionization+of+Proteins+with+Molecular+Masses+Exceeding+10000+Daltons.">Laser Desorption Ionization of Proteins with Molecular Masses Exceeding 10000 Daltons.</a> Anal. Chem. 60, 2299-2301 (1988).</li><li>Beavis, R. C., Chait, B. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Velocity+Distributions+of+Intact+High+Mass+Polypeptide+Molecule+Ions+Produced+by+Matrix+Assisted+Laser+Desorption.">Velocity Distributions of Intact High Mass Polypeptide Molecule Ions Produced by Matrix Assisted Laser Desorption.</a> Chem. Phys. Lett. 181, 479-484 (1991).</li><li>Beavis, R. C., Chaudhary, T., Chait, B. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alpha-Cyano-4-Hydroxycinnamic+Acid+as+a+Matrix+for+Matrix-Assisted+Laser+Desorption+Mass-Spectrometry.">Alpha-Cyano-4-Hydroxycinnamic Acid as a Matrix for Matrix-Assisted Laser Desorption Mass-Spectrometry.</a> Org. Mass Spectrom. 27, 156-158 (1992).</li><li>Ehring, H., Karas, M., Hillenkamp, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+Photoionization+and+Photochemistry+in+Ionization+Processes+of+Organic-Molecules+and+Relevance+for+Matrix-Assisted+Laser+Desorption+Ionization+Mass-Spectrometry.">Role of Photoionization and Photochemistry in Ionization Processes of Organic-Molecules and Relevance for Matrix-Assisted Laser Desorption Ionization Mass-Spectrometry.</a> Org. Mass Spectrom. 27, 472-480 (1992).</li><li>Strupat, K., Karas, M., Hillenkamp, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=2,5-Dihydroxybenzoic+Acid+-+a+New+Matrix+for+Laser+Desorption+Ionization+Mass-Spectrometry.">2,5-Dihydroxybenzoic Acid - a New Matrix for Laser Desorption Ionization Mass-Spectrometry.</a> Int. J. Mass Spectrom. Ion Process. 111, 89-102 (1991).</li><li>Hu, H., Larson, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaporation+of+a+Sessile+Droplet+on+a+Substrate.">Evaporation of a Sessile Droplet on a Substrate.</a> J. Phys. Chem. B. 106, 1334-1344 (2002).</li><li>Deegan, R. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capillary+Flow+as+the+Cause+of+Ring+Stains+from+Dried+Liquid+Drops.">Capillary Flow as the Cause of Ring Stains from Dried Liquid Drops.</a> Nature. 389, 827-829 (1997).</li><li>Hu, J. -. B., Chen, Y. -. C., Urban, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coffee-Ring+Effects+in+Laser+Desorption/Ionization+Mass+Spectrometry.">Coffee-Ring Effects in Laser Desorption/Ionization Mass Spectrometry.</a> Anal. Chim. Acta. 766, 77-82 (2013).</li><li>Schwartz, S. A., Reyzer, M. L., Caprioli, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+Tissue+Analysis+Using+Matrix-Assisted+Laser+Desorption/Ionization+Mass+Spectrometry:+Practical+Aspects+of+Sample+Preparation.">Direct Tissue Analysis Using Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry: Practical Aspects of Sample Preparation.</a> J. Mass Spectrom. 38, 699-708 (2003).</li><li>Hu, H., Larson, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Marangoni+Effect+Reverses+Coffee-Ring+Depositions.">Marangoni Effect Reverses Coffee-Ring Depositions.</a> J. Phys. Chem. B. 110, 7090-7094 (2006).</li><li>Bhardwaj, R., Fang, X., Attinger, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pattern+Formation+During+the+Evaporation+of+a+Colloidal+Nanoliter+Drop:+A+Numerical+and+Experimental+Study.">Pattern Formation During the Evaporation of a Colloidal Nanoliter Drop: A Numerical and Experimental Study.</a> New J. Phys. 11, 075020 (2009).</li><li>Savino, R., Paterna, D., Favaloro, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Buoyancy+and+Marangoni+Effects+in+an+Evaporating+Drop.">Buoyancy and Marangoni Effects in an Evaporating Drop.</a> J Thermophys Heat Tr. 16, 562-574 (2002).</li><li>Probstein, R. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Surface Tension. in Physicochemical Hydrodynamics : An Introduction. , 305-361 (1994).</li><li>Lai, Y. -. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reducing+Spatial+Heterogeneity+of+MALDI+Samples+with+Marangoni+Flows+During+Sample+Preparation.">Reducing Spatial Heterogeneity of MALDI Samples with Marangoni Flows During Sample Preparation.</a> J. Am. Soc. Mass Spectrom. 27, 1314-1321 (2016).</li><li>Hsiao, C. -. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comprehensive+Molecular+Imaging+of+Photolabile+Surface+Samples+with+Synchronized+Dual-Polarity+Time-of-Flight+Mass+Spectrometry.">Comprehensive Molecular Imaging of Photolabile Surface Samples with Synchronized Dual-Polarity Time-of-Flight Mass Spectrometry.</a> Rapid Commun. Mass Spectrom. 25, 834-842 (2011).</li><li>Vorm, O., Roepstorff, P., Mann, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+Resolution+and+Very+High-Sensitivity+in+MALDI+TOF+of+Matrix+Surfaces+Made+by+Fast+Evaporation.">Improved Resolution and Very High-Sensitivity in MALDI TOF of Matrix Surfaces Made by Fast Evaporation.</a> Anal. Chem. 66, 3281-3287 (1994).</li><li>Gabriel, S. J., Schwarzinger, C., Schwarzinger, B., Panne, U., Weidner, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Matrix+Segregation+as+the+Major+Cause+for+Sample+Inhomogeneity+in+MALDI+Dried+Droplet+Spots.">Matrix Segregation as the Major Cause for Sample Inhomogeneity in MALDI Dried Droplet Spots.</a> J. Am. Soc. Mass Spectrom. 25, 1356-1363 (2014).</li><li>Mampallil, D., Eral, H. B., van den Ende, D., Mugele, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+of+Evaporating+Complex+Fluids+through+Electrowetting.">Control of Evaporating Complex Fluids through Electrowetting.</a> Soft Matter. 8, 10614-10617 (2012).</li></ol>

Based on previous theoretical predictions, temperature-induced hydrodynamic flows within droplets can overcome outward capillary flows induced by solvent evaporation. The efficiency of such internal recirculation of molecules is enhanced when the temperature gradients within a droplet increase. According to the predicted results, when keeping the sample plate temperature under 5 &#176;C while maintaining its surroundings at ambient temperature, the average velocity of recirculation flows within the droplet is about 4 tim...

Mass spectrometry (MS) is one of the most important analytical techniques for analyzing the molecular compositions of complex samples. Among all the ionization methods used in MS, matrix-assisted laser desorption/ionization (MALDI) is the most sensitive and widely used method in bioanalytical applications.1 In comparison to other ionization techniques, MALDI has the highest sensitivity and high tolerance to salt contaminants. Such analytical properties make MALDI the first choice for carbohydrate analysis and many proteomics applications. However, sample preparation is a crucial step for obtaining high quality data in MALDI-MS.
The most commonly used sample preparation method for MALDI-MS is the dried-droplet method, in which sample droplets are deposited on a surface and dried under ambient conditions. This drying method is simple and generally effective.2-5 However, a common problem in the dried-droplet method is that the resultant analyte/matrix crystals normally distribute irregularly. In many cases, the crystals aggregate at the periphery of sample areas, resulting in the so-called ring-stain formation.6-8 The heterogeneous crystal morphologies affect the spatial distribution of analyte molecules, which results in severe fluctuation in ion signal over sample areas. Such severe signal fluctuations and poor data reproducibility are known as the "sweet spot" problem in MALDI-MS.9 Thus, there is a great need for reducing spatial heterogeneities in MALDI-MS dried droplet applications.
Hydrodynamic flows in the sample droplet play an important role in determining the spatial distribution of samples prepared with the dried-droplet method.10-12 It was found that the evaporation of solvent induces outward capillary flows within droplets, which are responsible for the ring-stain formation.7,10 In contrast, recirculation flows induced by tangential surface-tension gradients may counterbalance the outward capillary flows.13 If the recirculation flow speeds are higher than that of the outward capillary flows, the samples can be efficiently redistributed to reduce the heterogeneity problem.14
In this work, we demonstrate a detailed protocol for preparing samples with a simple drying chamber to induce efficient recirculation flows during droplet drying processes. Droplet drying conditions are precisely controlled, including the temperatures of the sample plate and its surroundings, and the relative humidity within the chamber. The model analytes include maltotriose and bradykinin chain (1-7). The matrix used for the demonstration is 2,4,6-trihydroxyacetophenone (THAP). The samples are examined with time-of-flight (TOF) MS, and the data are analyzed quantitatively to show the reduction of heterogeneity.

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			<td height="21" style="height:21px;width:303px;">Name of Reagent</td>
			<td style="width:157px;"></td>
			<td style="width:139px;"></td>
			<td style="width:191px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Detergent powder</td>
			<td style="width:157px;">Alconox</td>
			<td style="width:139px;">242985</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Methanol</td>
			<td style="width:157px;">Merck</td>
			<td style="width:139px;">106009</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Acetonitrile</td>
			<td style="width:157px;">Merck</td>
			<td style="width:139px;">100003</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">2,4,6-trihydroxyacetophenone (THAP)</td>
			<td style="width:157px;">Sigma-Aldrich</td>
			<td style="width:139px;">T64602&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Bradykinin fragment (1-7)</td>
			<td style="width:157px;">Sigma-Aldrich</td>
			<td style="width:139px;">B1651</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Maltotriose</td>
			<td style="width:157px;">Sigma-Aldrich</td>
			<td style="width:139px;">47884</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Pipette tips</td>
			<td style="width:157px;">Mettler Toledo</td>
			<td style="width:139px;">17005091</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Microcentrifuge tube</td>
			<td style="width:157px;">Axygen</td>
			<td style="width:139px;">MCT-150-C</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;"></td>
			<td style="width:157px;"></td>
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			<td height="21" style="height:21px;width:303px;">Name of Equipment</td>
			<td style="width:157px;"></td>
			<td style="width:139px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Milli-Q water purification system</td>
			<td style="width:157px;">Millipore</td>
			<td style="width:139px;">ZMQS6VFT1</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Powder-free nitrile gloves</td>
			<td style="width:157px;">Microflex</td>
			<td style="width:139px;">SU-690</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">600 mL beaker</td>
			<td style="width:157px;">Duran</td>
			<td style="width:139px;">2110648</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Ultrasonic cleaner</td>
			<td style="width:157px;">Delta</td>
			<td style="width:139px;">DC300H</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Hygrometer</td>
			<td style="width:157px;">Wisewind</td>
			<td style="width:139px;">5330</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Nitrogen gas flowmeter</td>
			<td style="width:157px;">Dwyer</td>
			<td style="width:139px;">RMA-6-SSV</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">K-type thermocouples</td>
			<td style="width:157px;">Digitron</td>
			<td style="width:139px;">311-1670</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Centrifuge</td>
			<td style="width:157px;">Select BioProducts</td>
			<td style="width:139px;">Force Mini&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Pipette</td>
			<td style="width:157px;">Rainin</td>
			<td style="width:139px;">pipet-lite XLS</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Stereomicroscope</td>
			<td style="width:157px;">Olympus</td>
			<td style="width:139px;">SZX16</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">Temperature controllable drying chamber</td>
			<td style="width:157px;">this lab</td>
			<td style="width:139px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:303px;">Synchronized dual-polarity time-of-flight imaging mass spectrometer (DP-TOF IMS)</td>
			<td style="width:157px;">this lab</td>
			<td style="width:139px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:303px;">MALDI-TOF stainless steel sample target</td>
			<td style="width:157px;">this lab</td>
			<td style="width:139px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

preparation of homogeneous maldi samples for quantitative applications

This protocol demonstrates a simple sample preparation to reduce spatial heterogeneity in ion signals during matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The heterogeneity of ion signals is a severe problem in MALDI, which results in poor data reproducibility and makes MALDI unsuitable for quantitative analysis. By regulating sample plate temperature during sample preparation, thermal-induced hydrodynamic flows inside droplets of sample solution are able to reduce the heterogeneity problem. A room-temperature sample preparation chamber equipped with a temperature-regulated copper base block that holds MALDI sample plates facilitates precise control of the sample drying condition. After drying of sample droplets, the temperature of sample plates is returned to room temperature and removed from the chamber for subsequent mass spectrometric analysis. The areas of samples are examined with MALDI-imaging mass spectrometry to obtain the spatial distribution of all components in the sample. In comparison with the conventional dried-droplet method that prepares samples under ambient conditions without temperature control, the samples prepared with the method demonstrated herein show significantly better spatial distribution and signal intensity. According to observations using carbohydrate and peptide samples, decreasing substrate temperature while maintaining the surroundings at ambient temperature during the drying process can effectively reduce the heterogeneity of ion signals. This method is generally applicable to various combinations of samples and matrices.

The bright-field images as well as the MS images of maltotriose and bradykinin fragment (1-7) prepared with sample plate temperature of 5 and 25 &#176;C are shown in Figure 1. In the case of sodiated maltotriose, the ion signal mainly populates at the periphery of the sample area when it is prepared with a sample plate temperature of 25 &#176;C. By decreasing the sample plate temperature to 5 &#176;C, the signal populates homogeneously over the entire sample area. The onl...

Watch this Scientific Journal Video about Preparation of Homogeneous MALDI Samples for Quantitative Applications at JoVE.com

Preparation of Homogeneous MALDI Samples for Quantitative Applications

A protocol for reducing spatial heterogeneities of ion signals in MALDI mass spectrometry by regulating substrate temperature during sample drying processes is demonstrated.

This protocol demonstrates a simple sample preparation to reduce spatial heterogeneity in ion signals during matrix-assisted laser desorption/ionization ...

The overall goal of this sample preparation method from MALDI MS is to reduce the spatial heterogeneity in ion signals during MALDI MS.A well controlled drying environment was built to optimize the conventional dried-droplet method, by manipulating the hydrodynamic flows inside the sample droplet during the drying process. The main advantage of this technique is that the spatial heterogeneity of the ion signals for the sample prepared by the optimized dried-droplet method can be effectively reduced. Though this method can provide homogenous samples for the THAP Metric System.It can also be applied to other metric systems, such as alpha-Cyano-4-hydroxycinnamic acid. Generally, individuals new to this method were struggled because controlling the drying condition is not easy. To begin this procedure, open the door of a drying chamber and immediately place a previously cleaned sample plate on the copper-based block.Then, close the door. Manually adjust the gas-flow meter to set the nitrogen flow rate to 10 standard cubic feet per hour. Following this, fine-tune the gas-flow meter to ensure the relative humidity is always below 25%in the drying chamber, as measured by a hygrometer.Using K Type Thermocouples to monitor the temperature, adjust the water circulator temperature manually, until the sample plate reaches 5 degrees Celsius for the experiment. Ensure the required temperatures and the relative humidity are reached before sample deposition. Mix 0.25 microliters of 0.1 Molar THAP solution and 0.25 microliters of the desired analyte in a microcentrifuge tube.Vortex the sample for three seconds. Then, centrifuge the sample for two seconds to collect the solution at the bottom of the microcentrifuge tube. Following centrifugation, open the door of the drying chamber and carefully deposit 0.1 microliters of the solution on the sample plate with a pipette.Close the door immediately and wait for the sample droplet to dry out. When keeping the sample plate temperature lower than its surroundings, the average velocity of recirculation flows within the droplet is significantly increased to redistribute molecules. Sample deposition is the most critical step that determines data quality and reproducibility.The premixed sample solution needs to be deposit immediately on the sample plate to ensure the sample is crystallized under controlled condition. After drying, open the door. of the drying chamber.Then, set the water circulator temperature to 25 degrees Celsius. Once the sample plate temperature returns to 25 degrees Celsius, remove the sample plate from the drying chamber. Examine the sample morphology under a five times magnified Stereo microscope, and take a snapshot brightfield image.At this point, insert the sample plate into a MALDI Mass Spectrometer. Then, perform imaging mass spectrometry analysis. Select a characteristic mass peak from the mass list shown in the result window and click 2D to plot a two-dimensional ion image.Next, click the adjustment buttons in the pop-up window to determine the upper and lower limits of the signal intensity, to increase the image resolution, and click save a picture. Observe and compare the ion image with the previously acquired brightfield image to obtain the essential sample region. Now, click the null spots and the cracked regions in the ion image shown in the result window to fine-adjust the region to be analyzed.Click the find edge button to find the outer-most layer of the ion image. Following this, click deduct to save the ion abundance information of the outmost layer in a database, and remove this layer from the ion image simultaneously. After repeating the previous steps until the center of the ion image is defined, click and select all the checkboxes in the output data list and click export to export the data.Finally, open the exported data using spreadsheet software to calculate the average ion abundance of every layer, to obtain the spatial distribution information of ions. In the brightfield and MALDI images of maltotriose, the ion signal of the sodiated form mainly populates at the periphery of the sample area, when it is prepared with a sample plate temperature of 25 degrees Celsius. By decreasing the temperature to five degrees Celsius, the signal populates homogeneously over the entire sample area, suggesting that preparing samples under a lower sample plate temperature can significantly redistribute the molecules and reduce heterogeneity.The protonated bradykinin fragment ion image shows a similar trend as the sodiated maltotriose. Statistical analyses show that the heterogeneity of ion signals obtained under a sample plate temperature of 5 degrees Celsius reduces by 60 to 80 percent, with respect to that under 25 degrees Celsius. In the case of sodiated maltotriose, with a sample plate temperature of 25 degrees Celsius, the signal intensities at the centers are much lower than those with the temperature of 5 degrees Celsius.The protonated bradykinin fragment shows less variation when decreasing the sample plate temperature from 25 to 5 degrees Celsius. While attempting this drying method, the temperatures and relative humidity in the drying chamber need to be carefully controlled and monitored. Once mastered, a sample prepared by this technique can be done in 30 minutes if it is performed properly.After it's development, this technique paved the way for researchers in the field of MALDI MS to explore quantitative analysis for dried-droplet samples. After watching this video, you should have a good understanding of how to prepare homogeneous dried-droplet samples for MALDI MS analysis.

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Biochemistry

Optimal Preparation of Formalin Fixed Samples for Peptide Based Matrix Assisted Laser Desorption/Ionization Mass Spectrometry Imaging Workflows

The use of matrix-assisted laser desorption/ionization, mass spectrometry imaging (MALDI MSI) has rapidly expanded, since this technique analyzes a host of biomolecules from drugs and lipids to N-glycans. Although various sample preparation techniques exist, detecting peptides from formaldehyde preserved tissues remains one of the most difficult challenges for this type of mass spectrometric analysis. For this reason, we have created and optimized a robust methodology that preserves the spatial information contained within the sample, while eliciting the greatest number of ionizable peptides. We have also aimed to achieve this in a cost effective and simple way, thereby eliminating potential bias or preparation error, which can occur when using automated instrumentation. The end result is a reproducible and inexpensive protocol.

This protocol describes a reproducible and reliable method for the sublimation-based preparation of formalin fixed tissue destined for imaging mass spectrometry.

The use of matrix-assisted laser desorption/ionization, mass spectrometry imaging (MALDI MSI) has rapidly expanded, since this technique analyzes a host ...

Proofreading and DNA Repair Assay Using Single Nucleotide Extension and MALDI-TOF Mass Spectrometry Analysis

The maintenance of the genome and its faithful replication is paramount for conserving genetic information. To assess high fidelity replication, we have developed a simple non-labeled and non-radio-isotopic method using a matrix-assisted laser desorption ionization with time-of-flight (MALDI-TOF) mass spectrometry (MS) analysis for a proofreading study. Here, a DNA polymerase [e.g., the Klenow fragment (KF) of Escherichia coli DNA polymerase I (pol I) in this study] in the presence of all four dideoxyribonucleotide triphosphates is used to process a mismatched primer-template duplex. The mismatched primer is then proofread/extended and subjected to MALDI-TOF MS. The products are distinguished by the mass change of the primer down to single nucleotide variations. Importantly, a proofreading can also be determined for internal single mismatches, albeit at different efficiencies. Mismatches located at 2-4-nucleotides (nt) from the 3' end were efficiently proofread by pol I, and a mismatch at 5 nt from the primer terminus showed only a partial correction. No proofreading occurred for internal mismatches located at 6 - 9 nt from the primer 3' end. This method can also be applied to DNA repair assays (e.g., assessing a base-lesion repair of substrates for the endo V repair pathway). Primers containing 3' penultimate deoxyinosine (dI) lesions could be corrected by pol I. Indeed, penultimate T-I, G-I, and A-I substrates had their last 2 dI-containing nucleotides excised by pol I before adding a correct ddN 5'-monophosphate (ddNMP) while penultimate C-I mismatches were tolerated by pol I, allowing the primer to be extended without repair, demonstrating the sensitivity and resolution of the MS assay to measure DNA repair.

A non-labeled, non-radio-isotopic method for DNA polymerase proofreading and a DNA repair assay was developed by using high-resolution MALDI-TOF mass spectrometry and a single nucleotide extension strategy. The assay proved to be very specific, simple, rapid, and easy to perform for proofreading and repair patches shorter than 9-nucleotides.

The maintenance of the genome and its faithful replication is paramount for conserving genetic information. To assess high fidelity replication, we have ...

Use of Microscale Thermophoresis to Measure Protein-Lipid Interactions

The ability to determine the binding affinity of lipids to proteins is an essential part of understanding protein-lipid interactions in membrane trafficking, signal transduction and cytoskeletal remodeling. Classic tools for measuring such interactions include surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC). While powerful tools, these approaches have setbacks. ITC requires large amounts of purified protein as well as lipids, which can be costly and difficult to produce. Furthermore, ITC as well as SPR are very time consuming, which could add significantly to the cost of performing these experiments. One way to bypass these restrictions is to use the relatively new technique of microscale thermophoresis (MST). MST is fast and cost effective using small amounts of sample to obtain a saturation curve for a given binding event. There currently are two types of MST systems available. One type of MST requires labeling with a fluorophore in the blue or red spectrum. The second system relies on the intrinsic fluorescence of aromatic amino acids in the UV range. Both systems detect the movement of molecules in response to localized induction of heat from an infrared laser. Each approach has its advantages and disadvantages. Label-free MST can use untagged native proteins; however, many analytes, including pharmaceuticals, fluoresce in the UV range, which can interfere with determination of accurate KD values. In comparison, labeled MST allows for a greater diversity of measurable pairwise interactions utilizing fluorescently labeled probes attached to ligands with measurable absorbances in the visible range as opposed to UV, limiting the potential for interfering signals from analytes.

Microscale thermophoresis obtains binding constants quickly at low material cost. Either labeled or label free microscale thermophoresis is commercially available; however, label free thermophoresis is not capable of the diversity of interaction measurements that can be performed using fluorescent labels. We provide a protocol for labeled thermophoresis measurements.

The ability to determine the binding affinity of lipids to proteins is an essential part of understanding protein-lipid interactions in membrane ...

Quantitative Analysis of the Cellular Lipidome of Saccharomyces Cerevisiae Using Liquid Chromatography Coupled with Tandem Mass Spectrometry

Lipids are structurally diverse amphipathic molecules that are insoluble in water. Lipids are essential contributors to the organization and function of biological membranes, energy storage and production, cellular signaling, vesicular transport of proteins, organelle biogenesis, and regulated cell death. Because the budding yeast Saccharomyces cerevisiae is a unicellular eukaryote amenable to thorough molecular analyses, its use as a model organism helped uncover mechanisms linking lipid metabolism and intracellular transport to complex biological processes within eukaryotic cells. The availability of a versatile analytical method for the robust, sensitive, and accurate quantitative assessment of major classes of lipids within a yeast cell is crucial for getting deep insights into these mechanisms. Here we present a protocol to use liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) for the quantitative analysis of major cellular lipids of S. cerevisiae. The LC-MS/MS method described is versatile and robust. It enables the identification and quantification of numerous species (including different isobaric or isomeric forms) within each of the 10 lipid classes. This method is sensitive and allows identification and quantitation of some lipid species at concentrations as low as 0.2 pmol/&#181;L. The method has been successfully applied to assessing lipidomes of whole yeast cells and their purified organelles. The use of alternative mobile phase additives for electrospray ionization mass spectrometry in this method can increase the efficiency of ionization for some lipid species and can be therefore used to improve their identification and quantitation.

Quantitative Analysis of the Cellular Lipidome of Saccharomyces Cerevisiae Using Liquid Chromatography Coupled with Tandem Mass Spectrometry

We present a protocol using liquid chromatography coupled with tandem mass spectrometry to identify and quantify major cellular lipids in Saccharomyces cerevisiae. The described method for a quantitative assessment of major lipid classes within a yeast cell is versatile, robust, and sensitive.

Lipids are structurally diverse amphipathic molecules that are insoluble in water. Lipids are essential contributors to the organization and function of ...

Ubiquitin Chain Analysis by Parallel Reaction Monitoring

Assessment of the global profile of ubiquitin chain topologies within a proteome is of interest to answer a wide range of biological questions. The protocol outlined here takes advantage of the di-glycine (-GG) modification left after the tryptic digestion of ubiquitin incorporated in a chain. By quantifying these topology-characteristic peptides the relative abundance of each ubiquitin chain topology can be determined. The steps required to quantify these peptides by a parallel reaction monitoring experiment are reported taking into consideration the stabilization of ubiquitin chains. Preparation of heavy controls, cell lysis, and digestion are described along with the appropriate mass spectrometer setup and data analysis workflow. An example data set with perturbations in ubiquitin topology is presented, accompanied by examples of how optimization of the protocol can affect results. By following the steps outlined, a user will be able to perform a global assessment of the ubiquitin topology landscape within their biological context.

This method describes the assessment of global changes in ubiquitin chain topology. The assessment is performed by the application of a mass spectrometry-based targeted proteomics approach.

Assessment of the global profile of ubiquitin chain topologies within a proteome is of interest to answer a wide range of biological questions. The ...

Quantitative Metabolomics of Saccharomyces Cerevisiae Using Liquid Chromatography Coupled with Tandem Mass Spectrometry

Metabolomics is a methodology used for the identification and quantification of many low-molecular-weight intermediates and products of metabolism within a cell, tissue, organ, biological fluid, or organism. Metabolomics traditionally focuses on water-soluble metabolites. The water-soluble metabolome is the final product of a complex cellular network that integrates various genomic, epigenomic, transcriptomic, proteomic, and environmental factors. Hence, the metabolomic analysis directly assesses the outcome of the action for all these factors in a plethora of biological processes within various organisms. One of these organisms is the budding yeast Saccharomyces cerevisiae, a unicellular eukaryote with the fully sequenced genome. Because S. cerevisiae is amenable to comprehensive molecular analyses, it is used as a model for dissecting mechanisms underlying many biological processes within the eukaryotic cell. A versatile analytical method for the robust, sensitive, and accurate quantitative assessment of the water-soluble metabolome would provide the essential methodology for dissecting these mechanisms. Here we present a protocol for the optimized conditions of metabolic activity quenching in and water-soluble metabolite extraction from S. cerevisiae cells. The protocol also describes the use of liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) for the quantitative analysis of the extracted water-soluble metabolites. The LC-MS/MS method of non-targeted metabolomics described here is versatile and robust. It enables the identification and quantification of more than 370 water-soluble metabolites with diverse structural, physical, and chemical properties, including different structural isomers and stereoisomeric forms of these metabolites. These metabolites include various energy carrier molecules, nucleotides, amino acids, monosaccharides, intermediates of glycolysis, and tricarboxylic cycle intermediates. The LC-MS/MS method of non-targeted metabolomics is sensitive and allows the identification and quantitation of some water-soluble metabolites at concentrations as low as 0.05 pmol/&#181;L. The method has been successfully used for assessing water-soluble metabolomes of wild-type and mutant yeast cells cultured under different conditions.

Quantitative Metabolomics of Saccharomyces Cerevisiae Using Liquid Chromatography Coupled with Tandem Mass Spectrometry

We present a protocol for the identification and quantitation of major classes of water-soluble metabolites in the yeast Saccharomyces cerevisiae. The described method is versatile, robust, and sensitive. It allows the separation of structural isomers and stereoisomeric forms of water-soluble metabolites from each other.

Metabolomics is a methodology used for the identification and quantification of many low-molecular-weight intermediates and products of metabolism within ...

Single-Molecule Imaging of EWS-FLI1 Condensates Assembling on DNA

The fusion genes resulting from chromosomal translocation have been found in many solid tumors or leukemia. EWS-FLI1, which belongs to the FUS/EWS/TAF15 (FET) family of fusion oncoproteins, is one of the most frequently involved fusion genes in Ewing sarcoma. These FET family fusion proteins typically harbor a low-complexity domain (LCD) of FET protein at their N-terminus and a DNA-binding domain (DBD) at their C-terminus. EWS-FLI1 has been confirmed to form biomolecular condensates at its target binding loci due to LCD-LCD and LCD-DBD interactions, and these condensates can recruit RNA polymerase II to enhance gene transcription. However, how these condensates are assembled at their binding sites remains unclear. Recently, a single-molecule biophysics method-DNA Curtains-was applied to visualize these assembling processes of EWS-FLI1 condensates. Here, the detailed experimental protocol and data analysis approaches are discussed for the application of DNA Curtains in studying the biomolecular condensates assembling on target DNA.

Here, we describe the use of the single-molecule imaging method, DNA Curtains, to study the biophysical mechanism of EWS-FLI1 condensates assembling on DNA.

The fusion genes resulting from chromosomal translocation have been found in many solid tumors or leukemia. EWS-FLI1, which belongs to the FUS/EWS/TAF15 ...

A Robust Single-Particle Cryo-Electron Microscopy (cryo-EM) Processing Workflow with cryoSPARC, RELION, and Scipion

Recent advances in both instrumentation and image processing software have made single-particle cryo-electron microscopy (cryo-EM) the preferred method for structural biologists to determine high-resolution structures of a wide variety of macromolecules. Multiple software suites are available to new and expert users for image processing and structure calculation, which streamline the same basic workflow: movies acquired by the microscope detectors undergo correction for beam-induced motion and contrast transfer function (CTF) estimation. Next, particle images are selected and extracted from averaged movie frames for iterative 2D and 3D classification, followed by 3D reconstruction, refinement, and validation. Because various software packages employ different algorithms and require varying levels of expertise to operate, the 3D maps they generate often differ in quality and resolution. Thus, users regularly transfer data between a variety of programs for optimal results. This paper provides a guide for users to navigate a workflow across the popular software packages: cryoSPARC v3, RELION-3, and Scipion 3 to obtain a near-atomic resolution structure of the adeno-associated virus (AAV). We first detail an image processing pipeline with cryoSPARC v3, as its efficient algorithms and easy-to-use GUI allow users to quickly arrive at a 3D map. In the next step, we use PyEM and in-house scripts to convert and transfer particle coordinates from the best quality 3D reconstruction obtained in cryoSPARC v3 to RELION-3 and Scipion 3 and recalculate 3D maps. Finally, we outline steps for further refinement and validation of the resultant structures by integrating algorithms from RELION-3 and Scipion 3. In this article, we describe how to effectively utilize three processing platforms to create a single and robust workflow applicable to a variety of data sets for high-resolution structure determination.

A Robust Single-Particle Cryo-Electron Microscopy cryo-EM Processing Workflow with cryoSPARC, RELION, and Scipion

This article describes how to effectively utilize three cryo-EM processing platforms, i.e., cryoSPARC v3, RELION-3, and Scipion 3, to create a single and robust workflow applicable to a variety of single-particle data sets for high-resolution structure determination.

Recent advances in both instrumentation and image processing software have made single-particle cryo-electron microscopy (cryo-EM) the preferred method ...

Identification of RNA Fragments Resulting from Enzymatic Degradation using MALDI-TOF Mass Spectrometry

RNA is a biopolymer present in all domains of life, and its interactions with other molecules and/or reactive species, e.g., DNA, proteins, ions, drugs, and free radicals, are ubiquitous. As a result, RNA undergoes various reactions that include its cleavage, degradation, or modification, leading to biologically relevant species with distinct functions and implications. One example is the oxidation of guanine to 7,8-dihydro-8-oxoguanine (8-oxoG), which may occur in the presence of reactive oxygen species (ROS). Overall, procedures that characterize such products and transformations are largely valuable to the scientific community. To this end, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry is a widely used method. The present protocol describes how to characterize RNA fragments formed after enzymatic treatment. The chosen model uses a reaction between RNA and the exoribonuclease Xrn-1, where enzymatic digestion is halted at oxidized sites. Two 20-nucleotide long RNA sequences [5&#39;-CAU GAA ACA A(8-oxoG)G CUA AAA GU] and [5&#39;-CAU GAA ACA A(8-oxoG)(8-oxoG) CUA AAA GU] were obtained via solid-phase synthesis, quantified by UV-vis spectroscopy, and characterized via MALDI-TOF. The obtained strands were then (1) 5&#39;-phosphorylated and characterized via MALDI-TOF; (2) treated with Xrn-1; (3) filtered and desalted; (4) analyzed via MALDI-TOF. This experimental setup led to the unequivocal identification of the fragments associated with the stalling of Xrn-1: [5&#39;-H2PO4-(8-oxoG)G CUA AAA GU], [5&#39;-H2PO4-(8-oxoG)(8-oxoG) CUA AAA GU], and [5&#39;-H2PO4-(8-oxoG) CUA AAA GU]. The described experiments were carried out with 200 picomols of RNA (20 pmol used for MALDI analyses); however, lower amounts may result in detectable peaks with spectrometers using laser sources with more power than the one used in this work. Importantly, the described methodology can be generalized and potentially extended to product identification for other processes involving RNA and DNA, and may aid in the characterization/elucidation of other biochemical pathways.

MALDI-TOF was used to characterize fragments obtained from the reactivity between oxidized RNA and the exoribonuclease Xrn-1. The present protocol describes a methodology that can be applied to other processes involving RNA and/or DNA.

RNA is a biopolymer present in all domains of life, and its interactions with other molecules and/or reactive species, e.g., DNA, proteins, ions, drugs, ...

A Detailed Guide for Preparing Hard Palm Seeds for MALDI-IMS Analysis

Preparation of Hard Palm Seeds for Matrix-Assisted Laser Desorption/Ionization-Imaging Mass Spectrometry Analysis

Matrix-assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS) is applied to identify compounds in their native environments. Currently, MALDI-IMS is frequently used in clinical analysis. Still, an excellent perspective exists for better applying this technique to understand chemical compounds&#39; physiological information in plant tissues. However, preparation may be challenging for specific samples from botanical materials, as MALDI-IMS requires thin slices (12-20 &#181;m) for appropriate data acquisition and successful analysis. In this sense, previously, we developed a sample preparation protocol to obtain thin sections of Euterpe oleracea (a&#231;a&#237; palm) hard seeds, enabling their molecular mapping by MALDI-IMS.
Here, we show that the developed protocol is suitable for preparing other seeds from the same genus. Briefly, the protocol was based on submerging the seeds in deionized water for 24 h, embedding samples with gelatin, and sectioning them in an acclimatized cryostat. Then, for matrix deposition, an xy motion platform was coupled to an electrospray ionization&#160;(ESI) needle spray using a 1:1 (v/v) 2,5-dihydroxybenzoic acid (DHB) and methanol solution with 0.1% trifluoroacetic acid at 30 mg/mL. E. precatoria and E. edulis seed data were processed using software to map their metabolite patterns.
Hexose oligomers were mapped within sample slices to prove the adequacy of the protocol for those samples, as it is known that those seeds contain large amounts of mannan, a polymer of the hexose mannose. As a result, peaks of hexose oligomers, represented by [M + K]+ adducts of (&#916; = 162 Da), were identified. Thus, the sample preparation protocol, previously developed tailor-made for E. oleracea seeds, also enabled MALDI-IMS analysis of two other hard palm seeds. In short, the method could constitute a valuable tool for research in the morpho-anatomy and physiology of botanical materials, especially from cut-resistant samples.

Author Spotlight: A Tailor-Made Sample Preparation Approach for Enhanced MALDI-IMS Analysis of Hard Palm Seeds

This protocol aimed to describe detailed guidance on the preparation of hard seed sample sections with low water content for MALDI-IMS analysis, maintaining analytes' original distribution and abundance and providing high-quality signal and spatial resolution.