Name: enabling real-time compensation in fast photochemical oxidations of proteins for the determination of protein topography changes
Uploaded: 2020-09-01T13:00:00
Description: Watch this Scientific Journal Video about Enabling Real-Time Compensation in Fast Photochemical Oxidations of Proteins for the Determination of Protein Topography Changes at JoVE.com

We acknowledge research funding from the National Institute of General Medical Sciences grant R43GM125420-01to support commercial development of a benchtop FPOP device and R01GM127267 for the development of standardization and dosimetry protocols for high-energy FPOP.

1. Prepare the Optical Bench and the Capillary for FPOP
CAUTION: KrF excimer lasers are extreme eye hazards, and direct or reflected light can cause permanent eye damage. Always wear appropriate eye protection, avoid the presence of any reflective objects near the beam path when possible, and use engineering controls to prevent unauthorized access to an active laser and to restrain any stray reflections.
<ol>
	<li>Prepare the FPOP optical bench.
	<ol>
		<li>Turn on the laser to warm up. Set ...

Mass spectrometry-based structural techniques, including hydrogen-deuterium exchange, chemical cross-linking, covalent labeling, and native spray mass spectrometry and ion mobility have been rapidly growing in popularity due to their flexibility, sensitivity, and ability to handle complex mixtures. FPOP boasts several advantages that has boosted its popularity in the area of mass spectrometry-based structural techniques. Like most covalent labeling strategies, it provides a stable chemical snapshot of protein topography ...

Fast photochemical oxidation of proteins (FPOP) is an emerging technique for the determination of protein topographical changes by ultra-fast covalent modification of the solvent-exposed surface area of proteins followed by detection by LC-MS1. FPOP generates a high concentration of hydroxyl radicals in situ by UV laser flash photolysis of hydrogen peroxide. These hydroxyl radicals are very reactive and short lived, consumed on roughly a microsecond timescale under FPOP conditions2. These hydroxyl radicals diffuse through water and oxidize various organic components in solution at kinetic rates generally ranging from fast (~106 M-1 s-1) to diffusion-controlled3. When the hydroxyl radical encounters a protein surface, the radical will oxidize the amino acid side chains on the protein surface, resulting in a mass shift of that amino acid (most commonly the net addition of one oxygen atom)4. The rate of the oxidation reaction at any amino acid depends on two factors: the inherent reactivity of that amino acid (which depends on the side chain and the sequence context)4,5 and the accessibility of that side chain to the diffusing hydroxyl radical, which closely correlates to the average solvent accessible surface area6,7. All of the standard amino acids except glycine have been observed as labeled by these highly reactive hydroxyl radicals in FPOP experiments, albeit at widely differing yields; in practice, Ser, Thr, Asn, and Ala are rarely seen as oxidized in most samples except under high radical doses and identified by careful and sensitive targeted ETD fragmentation8,9. After oxidation, samples are quenched to remove hydrogen peroxide and secondary oxidants (superoxide, singlet oxygen, peptidyl hydroperoxides, etc.) The quenched samples are then proteolytically digested to generate mixtures of oxidized peptides, where the structural information is frozen as a chemical &#8220;snapshot&#8221; in the patterns of oxidation products of the various peptides (Figure 1). Liquid chromatography coupled to mass spectrometry (LC-MS) is used to measure the amount of oxidation of amino acids in a given proteolytic peptide based on the relative intensities of the oxidized and unoxidized versions of that peptide. By comparing this oxidative footprint of the same protein obtained under different conformational conditions (e.g., ligand-bound versus ligand-free), differences in the amount of oxidation of a given region of the protein can be directly correlated with differences in the solvent-accessible surface area of that region6,7. The ability to provide protein topographical information makes FPOP an attractive technology for the higher-order structure determination of proteins, including in protein therapeutic discovery and development10,11.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61580/61580fig01.jpg" /> 
Figure 1: Overview of FPOP.&#160;The surface of the protein is covalently modified by highly reactive hydroxyl radicals. The hydroxyl radicals will react with amino acid side chains of the protein at a rate that is strongly influenced by the solvent accessibility of the side chain. Topographical changes (for example, due to the binding of a ligand as shown above) will protect amino acids in the region of interaction from reacting with hydroxyl radicals, resulting in a decrease in the intensity of modified peptide in the LC-MS signal. <a href="https://www.jove.com/files/ftp_upload/61580/61580fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Different constituents present in the FPOP solution (e.g., ligands, excipients, buffers) have different scavenging activity towards the hydroxyl radicals generated upon the laser photolysis of hydrogen peroxide3. Similarly, a small change in peroxide concentration, laser fluence, and buffer composition may change the effective radical dose, making the reproduction of FPOP data challenging across the samples and between different labs. Therefore, it is important to be able to compare the hydroxyl radical dose available to react with protein in each sample using one of several available hydroxyl radical dosimeters12,13,14,15,16. Hydroxyl radical dosimeters act by competing with the analyte (and with all scavengers in solution) for the pool of hydroxyl radicals; the effective dose of hydroxyl radicals is measured by measuring the amount of oxidation of the dosimeter. Note that &#8220;effective hydroxyl radical dose&#8221; is a function of both the initial concentration of hydroxyl radical generated and the half-life of the radical. These two parameters are partially dependent on one another, making the theoretical kinetic modeling somewhat complex (Figure 2). Two samples could have wildly different initial radical half-lives while still maintaining the same effective radical dose by changing the initial concentration of hydroxyl radical formed; they will still generate identical footprints17. Adenine13 and Tris12 are convenient hydroxyl radical dosimeters because their level of oxidation can be measured by UV spectroscopy in real-time, allowing for researchers to quickly identify when there is a problem with effective hydroxyl radical dose and to troubleshoot their problem. To solve this issue, an inline dosimeter located in the flow system directly after the site of irradiation that can monitor the signal from adenine absorbance changes in real-time is important. This helps in carrying out FPOP experiments in buffers or any other excipient with widely differing levels of hydroxyl radical scavenging capacity17. This radical dosage compensation can be performed in real-time, yielding statistically indistinguishable results for the same conformer by adjusting the effective radical dose.
In this protocol, we have detailed procedures for performing a typical FPOP experiment with radical dosage compensation using adenine as an internal optical radical dosimeter. This method allows investigators to compare footprints across FPOP conditions that have different scavenging capacity by performing compensation in real-time.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61580/61580fig02.jpg" /> 
Figure 2: Kinetic simulation of dosimetry-based compensation.&#160;1 mM adenine dosimeter response is measured in 5 &#181;M lysozyme analyte with a 1 mM initial hydroxyl radical concentration (&#9642;OH t1/2=53 ns), and set as a target dosimeter response (black). Upon the addition of 1 mM of the scavenger excipient histidine, the dosimeter response (blue) decreases along with the amount of protein oxidation in a proportional manner (cyan). The half-life of the hydroxyl radical also decreases (&#9642;OH t1/2=39 ns). When the amount of hydroxyl radical generated is increased to give an equivalent yield of oxidized dosimeter in the sample with 1 mM histidine scavenger as achieved with 1 mM hydroxyl radical in the absence of scavenger (red), the amount of protein oxidation that occurs similarly becomes identical (magenta), while the hydroxyl radical half-life decreases even further (&#9642;OH t1/2=29 ns). Adapted with permission from Sharp J.S., Am Pharmaceut Rev 22, 50-55, 2019. <a href="https://www.jove.com/files/ftp_upload/61580/61580fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table>
	<tbody>
		<tr>
			<td>Adenine</td>
			<td>Acros Organics</td>
			<td>147440250</td>
			<td>Soluble in water upto 3.5 mM</td>
		</tr>
		<tr>
			<td>Aperture</td>
			<td>Edmund Optics</td>
			<td>39-905</td>
			<td>1000 &#956;m Aperture Diameter, Gold-Plated Copper Aperture</td>
		</tr>
		<tr>
			<td>Aperture holder</td>
			<td>Edmund Optics</td>
			<td>53-287</td>
			<td>25.8mm Outer Diameter, Precision Pinhole Mount</td>
		</tr>
		<tr>
			<td>Catalse</td>
			<td>Sigma Aldrich</td>
			<td>C-40</td>
			<td>Catalase from bovine liver, lyophilized powder, &#8805;10,000 units/mg protein</td>
		</tr>
		<tr>
			<td>COMPex Pro laser</td>
			<td>Coherent</td>
			<td>1113836</td>
			<td>COMPexPRO 102, F-Vversion, KrF laser, No XeCl</td>
		</tr>
		<tr>
			<td>Dithiotheitol (DTT)</td>
			<td>Promega</td>
			<td>V3151</td>
			<td>DTT, Molecular Grade (DL-Dithiothreitol)</td>
		</tr>
		<tr>
			<td>Fraction collector</td>
			<td>GenNext Technologies, Inc.</td>
			<td>N/A</td>
			<td>Automated fraction collector</td>
		</tr>
		<tr>
			<td>Fused silica capillay</td>
			<td>Molex</td>
			<td>1068150023</td>
			<td>Polymicro Flexible Fused Silica Capillary Tubing, Inner Diameter 100 &#181;m, Outer Diameter 375 &#181;m, TSP100375</td>
		</tr>
		<tr>
			<td>Glutamine</td>
			<td>Acros Organics</td>
			<td>119951000</td>
			<td>L(+)-Glutamine, 99%</td>
		</tr>
		<tr>
			<td>Holder for lens</td>
			<td>Edmund Optics</td>
			<td>03-668</td>
			<td>53 mm Outer Diameter, Three-Screw Adjustable Ring Mount</td>
		</tr>
		<tr>
			<td>Hydrogen peroxide</td>
			<td>Fisher Scientific</td>
			<td>H325-100</td>
			<td>Hydrogen Peroxide, 30% (Certified ACS), Fisher Chemical</td>
		</tr>
		<tr>
			<td>LC-MS/MS system</td>
			<td>Thermo Scientific</td>
			<td>IQLAAEGAAPFADBMBCX</td>
			<td>Dionex Ultimate 3000 coupled to Orbitap Fusion Tribrid mass spectrometer</td>
		</tr>
		<tr>
			<td>Mas spec grade Acetonitrile</td>
			<td>Fisher Scientific</td>
			<td>A955-1</td>
			<td>Acetonitrile, Optima LC/MS Grade, Fisher Chemical</td>
		</tr>
		<tr>
			<td>Mass spec grade formic acid</td>
			<td>Fisher Scientific</td>
			<td>A117-50</td>
			<td>Formic Acid, 99.0+%, Optima&#8482; LC/MS Grade, Fisher Chemical</td>
		</tr>
		<tr>
			<td>Mass spec grade water</td>
			<td>Fisher Scientific</td>
			<td>W6-4</td>
			<td>Water, Optima LC/MS Grade, Fisher Chemical</td>
		</tr>
		<tr>
			<td>MES buffer</td>
			<td>Sigma Aldrich</td>
			<td>M0164</td>
			<td>MES hemisodium salt</td>
		</tr>
		<tr>
			<td>Methionine amide</td>
			<td>Bachem</td>
			<td>4000594.0005</td>
			<td>H-met-NH2.HCl</td>
		</tr>
		<tr>
			<td>Micro V clamp</td>
			<td>Thor Labs</td>
			<td>VK250</td>
			<td>Micro V-clamp with stainless steel blades</td>
		</tr>
		<tr>
			<td>Motorized stage</td>
			<td>Edmund Optics</td>
			<td>68-638</td>
			<td>50mm Travel Motorized Stage System with Manual Control</td>
		</tr>
		<tr>
			<td>Nano C18 colum</td>
			<td>Thermo Scientific</td>
			<td>164534</td>
			<td>Acclaim PepMap 100 C18 HPLC Columns</td>
		</tr>
		<tr>
			<td>Optical bench</td>
			<td>Edmund Optics</td>
			<td>56-935</td>
			<td>18&#34; x 18&#34; breadboard</td>
		</tr>
		<tr>
			<td>Pioneer FPOP Module System</td>
			<td>GenNext Technologies, Inc.</td>
			<td>N/A</td>
			<td>Inline FPOP Radical Dosimetry System</td>
		</tr>
		<tr>
			<td>Post holder</td>
			<td>Edmund Optics</td>
			<td>58-979</td>
			<td>3&#34; Length, &#188;-20 Thread, Post Holder</td>
		</tr>
		<tr>
			<td>Sodium phosphate dibasic</td>
			<td>Fisher Scientific</td>
			<td>BP331-500</td>
			<td>Sodium Phosphate Dibasic Heptahydrate (Colorless-to-White Crystals), Fisher BioReagents</td>
		</tr>
		<tr>
			<td>Sodium phosphate monobasic</td>
			<td>Fisher Scientific</td>
			<td>BP330-500</td>
			<td>Sodium Phosphate Monobasic Monohydrate (Colorless-to-white Crystals), Fisher BioReagents</td>
		</tr>
		<tr>
			<td>Syringe</td>
			<td>Hamilton</td>
			<td>81065</td>
			<td>100 &#181;L, Model 1710 RN SYR, Small Removable NDL, 22s ga, 2 in, point style 3</td>
		</tr>
		<tr>
			<td>Syringe pump</td>
			<td>KD Scientific</td>
			<td>788101</td>
			<td>Legato&#160;101 syringe pump</td>
		</tr>
		<tr>
			<td>Trap C18 column</td>
			<td>Thermo Scientific</td>
			<td>160454</td>
			<td>Thermo Scientific&#160;Acclaim PepMap 100 C18 HPLC Columns</td>
		</tr>
		<tr>
			<td>Tris</td>
			<td>Sigma Aldrich</td>
			<td>252859</td>
			<td>Tris(hydroxymethyl)aminomethane</td>
		</tr>
		<tr>
			<td>Trypsin</td>
			<td>Promega</td>
			<td>V5111</td>
			<td>Sequencing Grade Modified Trypsin</td>
		</tr>
		<tr>
			<td>UV plano convex lens</td>
			<td>Edmund Optics</td>
			<td>84-285</td>
			<td>30 mm Dia. x 120 mm FL Uncoated, UV Plano-Convex Lens</td>
		</tr>
	</tbody>
</table>

enabling real-time compensation in fast photochemical oxidations of proteins for the determination of protein topography changes

Fast photochemical oxidation of proteins (FPOP) is a mass spectrometry-based structural biology technique that probes the solvent-accessible surface area of proteins. This technique relies on the reaction of amino acid side chains with hydroxyl radicals freely diffusing in solution. FPOP generates these radicals in situ by laser photolysis of hydrogen peroxide, creating a burst of hydroxyl radicals that is depleted on the order of a microsecond. When these hydroxyl radicals react with a solvent-accessible amino acid side chain, the reaction products exhibit a mass shift that can be measured and quantified by mass spectrometry. Since the rate of reaction of an amino acid depends in part on the average solvent accessible surface of that amino acid, measured changes in the amount of oxidation of a given region of a protein can be directly correlated to changes in the solvent accessibility of that region between different conformations (e.g., ligand-bound versus ligand-free, monomer vs. aggregate, etc.) FPOP has been applied in a number of problems in biology, including protein-protein interactions, protein conformational changes, and protein-ligand binding. As the available concentration of hydroxyl radicals varies based on many experimental conditions in the FPOP experiment, it is important to monitor the effective radical dose to which the protein analyte is exposed. This monitoring is efficiently achieved by incorporating an inline dosimeter to measure the signal from the FPOP reaction, with laser fluence adjusted in real-time to achieve the desired amount of oxidation. With this compensation, changes in protein topography reflecting conformational changes, ligand-binding surfaces, and/or protein-protein interaction interfaces can be determined in heterogeneous samples using relatively low sample amounts.

Comparison of the heavy chain peptide footprint of the adalimumab biosimilar in phosphate buffer and when heated at 55 &#176;C for 1 h show interesting results. Student&#8217;s t-test is used for the identification of peptides that are significantly changed in these two conditions (p &#8804; 0.05). The peptides 20-38, 99-125, 215-222, 223-252, 260-278, 376-413, and 414-420 show significant protection from solvent when the protein is heated to form aggregates (Figure 5)30</s...

Watch this Scientific Journal Video about Enabling Real-Time Compensation in Fast Photochemical Oxidations of Proteins for the Determination of Protein Topography Changes at JoVE.com

Enabling Real-Time Compensation in Fast Photochemical Oxidations of Proteins for the Determination of Protein Topography Changes

Fast photochemical oxidation of proteins is an emerging technique for the structural characterization of proteins. Different solvent additives and ligands have varied hydroxyl radical scavenging properties. To compare the protein structure in different conditions, real-time compensation of hydroxyl radicals generated in the reaction is required to normalize reaction conditions.

Fast photochemical oxidation of proteins (FPOP) is a mass spectrometry-based structural biology technique that probes the solvent-accessible surface area ...

The method facilitates measurement of protein confirmation and protein interactions. The buffer composition, sample purity and protein concentration requirements are flexible allowing the method to address challenging structural problems. This technique allows a compression of samples in a wide variety of different buffer systems.Using our dosimetry method, researchers can monitor how well their labeling reactions are working in real time. One application of this technology is in drug development because it allows researchers to test widely different drug formulations and how they affect protein structure. To prepare the FPOP optical bench.First turn on the laser and set the laser to external trigger, constant energy and no gas replacement. When the laser has warmed set the laser energy per pulse to between 80 to 120 milligrams per pulse and use a butane torch to gently burn the polyimide coding of the capillary at the spot at which the inline dosimeter will read the absorbent signal at 265 nanometers after laser exposure. Use a lint-free wipe and methanol to gently wipe the debris from the capillary and place the cleaned capillary through the beam path of the laser and into the inline dosimeter.Press the lever on the top of the inline dosimeter to open the hinge and remove the magnetic holders. Place the capillary in the machine groove of the inline dosimeter using the magnetic holders to keep the capillary in place and close the dosimeter hinge over the capillary pressing the hinge until the lever locks in place. Click the start flash button in the dosimetry software to begin firing the excimer laser and set the preset repetition rate between 10 to 20 Hertz in the dosimetry software with the laser firing move the motorized stage through its range of motion, ensuring that the beam stays centered on the aperture and that the silhouette of the capillary can be observed throughout.Then flush the capillary with water at 20 microliters per minute for at least one minute and click start data plus auto zero in the dosimeter software to zero the dosimeter to the water before beginning the data collection. To perform an FPOP experiment add two microliters of hydrogen peroxide to 18 microliters of FPOP solution and use a pipette to gently mix the solution quickly collect the solution at the bottom of the tube by centrifugation and immediately use a gas tight syringe to load the solution into a syringe pump. Click start pump and start data in the dosimeter software to start the flow on the syringe pump at the appropriate flow rate and use the inline dosimeter to monitor the real-time adenine reading until the absorbent signal at 265 nanometers stabilizes collecting the sample in a waste container.To start firing the laser at the preset repetition rate end energy click the start flash button in the dosimeter software and use the inline dosimeter to monitor the real-time adenine reading. The difference in the absorbance at 265 nanometers with the laser off and the laser on will be the delta absorbents at 265 nanometers reading. To ensure that comparable hydroxyl radicals are available to react with proteins across different samples.Compare the delta absorbents at 265 nanometers reading obtained with the inline dosimeter with the desire delta absorbents at 265 nanometers reading obtained from previous experiments or controls. If the reading is at the desired level collect the sample immediately after laser or radiation in the quench buffer. To compensate the effective radical dose to equalize the absorbance readings change the hydrogen peroxide concentration, change the laser energy per pulse or change the focal plane of the focusing lens to increase the laser fluence.To make a greater than 10 milli absorbance unit change in the delta absorbents reading remake the sample with more or less hydrogen peroxide and rerun the sample as demonstrated. To make a small change in the absorbance reading in real time, use the 50 millimeter motorized stage to adjust the position of the focusing lens to adjust the focal plane of the incident beam. To measure the effective amount of hydroxyl radical present in the sample after laser radiation monitor the adenine delta absorbents at 265 nanometers in real time with an inline UV capillary detector using the motorized stage to adjust the lens position until the delta absorbents at 265 nanometers reading is equal to the desired reading.Comparison of the heavy chain peptide footprint of the adilumumab biosimilar in phosphate buffer and after heating at 55 degrees Celsius for one hour reveals that the indicated peptide regions demonstrate significant protection from solvents when the protein is heated to form aggregates. Using an inline dosimeter in real time to monitor the difference in adenine absorbents before and after laser or radiation indicates that a comparable change in the adenine absorbents level is observed in MES buffer compared to phosphate buffer. While the average oxidation of the peptides is lower in the presence of MES buffer compared to phosphate buffer.However, as the laser fluence is increased to have an equal adenine dosimetry response the average peptide oxidation values are almost the same after FPOP and MES buffer and phosphate buffer. As the dosimetry reading is affected by the laser fluence peroxide concentration as well as the radical scavenger. Take care that the dosimetry response between the sample survey close to each other.Site directed mutagenesis is often used to probe sites protected in FPOP. This allows researchers to determine if changes are due to Alistair. This technique facilitates the comparison of proteins in different buffers or formulations allowing researchers to determine the effect of different additives on protein confirmation.

enabling-real-time-compensation-fast-photochemical-oxidations

Research

JoVE Journal

Biochemistry

Real-time Tracking of DNA Fragment Separation by Smartphone

Slab gel electrophoresis (SGE) is the most common method for the separation of DNA fragments; thus, it is broadly applied to the field of biology and others. However, the traditional SGE protocol is quite tedious, and the experiment takes a long time. Moreover, the chemical consumption in SGE experiments is very high. This work proposes a simple method for the separation of DNA fragments based on an SGE chip. The chip is made by an engraving machine. Two plastic sheets are used for the excitation and emission wavelengths of the optical signal. The fluorescence signal of the DNA bands is collected by smartphone. To validate this method, 50, 100, and 1,000 bp DNA ladders were separated. The results demonstrate that a DNA ladder smaller than 5,000 bp can be resolved within 12 min and with high resolution when using this method, indicating that it is an ideal substitute for the traditional SGE method.

Traditional slab gel electrophoresis (SGE) experiments require a complicated apparatus and high chemical consumption. This work presents a protocol that describes a low-cost method to separate DNA fragments within a short timeframe.

Slab gel electrophoresis (SGE) is the most common method for the separation of DNA fragments; thus, it is broadly applied to the field of biology and ...

Regeneration of Arrayed Gold Microelectrodes Equipped for a Real-Time Cell Analyzer

The label-free cell-based assay is advantageous for biochemical study because of it does not require the use of experimental animals. Due to its ability to provide more dynamic information about cells under physiological conditions than classical biochemical assays, this label-free real-time cell assay based on the electric impedance principle is attracting more attention during the past decade. However, its practical utilization may be limited due to the relatively expensive cost of measurement, in which costly consumable disposable gold microchips are used for the cell analyzer. In this protocol, we have developed a general strategy to regenerate arrayed gold microelectrodes equipped for a commercial label-free cell analyzer. The regeneration process includes trypsin digestion, rinsing with ethanol and water, and a spinning step. The proposed method has been tested and shown to be effective for the regeneration and repeated usage of commercial electronic plates at least three times, which will help researchers save on the high running cost of real-time cell assays.

This protocol describes a general strategy to regenerate commercial arrayed gold microelectrodes equipped for a label-free cell analyzer aimed at saving on the high running costs ofmicrochip-based assays. The regeneration process includes trypsin digestion, rinsing with ethanol and water, and a spinning step, which enables repeated usage of microchips.

The label-free cell-based assay is advantageous for biochemical study because of it does not require the use of experimental animals. Due to its ability ...

The Determination of Protease Specificity in Mouse Tissue Extracts by MALDI-TOF Mass Spectrometry: Manipulating PH to Cause Specificity Changes

Proteases have several biological functions, including protein activation/inactivation and food digestion. Identifying protease specificity is important for revealing protease function. The method proposed in this study determines protease specificity by measuring the molecular weight of unique substrates using Matrix-assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) mass spectrometry. The substrates contain iminobiotin, while the cleaved site consists of amino acids, and the spacer consists of polyethylene glycol. The cleaved substrate will generate a unique molecular weight using a cleaved amino acid. One of the merits of this method is that it may be carried out in one pot using crude samples, and it is also suitable for assessing multiple samples. In this article, we describe a simple experimental method optimized with samples extracted from mouse lung tissue, including tissue extraction, placement of digestive substrates into samples, purification of digestive substrates under different pH conditions, and measurement of the substrates&#39; molecular weight using MALDI-TOF mass spectrometry. In summary, this technique allows for the identification of protease specificity in crude samples derived from tissue extracts using MALDI-TOF mass spectrometry, which may easily be scaled up for multiple sample processing.

Here, we present a protocol to determine protease specificity in crude mouse tissue extracts using MALDI-TOF spectrometry.

Proteases have several biological functions, including protein activation/inactivation and food digestion. Identifying protease specificity is important ...

Covalent Immobilization of Proteins for the Single Molecule Force Spectroscopy

In recent years, atomic force microscopy (AFM) based single molecule force spectroscopy (SMFS) extended our understanding of molecular properties and functions. It gave us the opportunity to explore a multiplicity of biophysical mechanisms, e.g., how bacterial adhesins bind to host surface receptors in more detail. Among other factors, the success of SMFS experiments depends on the functional and native immobilization of the biomolecules of interest on solid surfaces and AFM tips. Here, we describe a straightforward protocol for the covalent coupling of proteins to silicon surfaces using silane-PEG-carboxyls and the well-established N-hydroxysuccinimid/1-ethyl-3-(3-dimethyl-aminopropyl)carbodiimid (EDC/NHS) chemistry in order to explore the interaction of pilus-1 adhesin RrgA from the Gram-positive bacterium Streptococcus pneumoniae (S. pneumoniae) with the extracellular matrix protein fibronectin (Fn). Our results show that the surface functionalization leads to a homogenous distribution of Fn on the glass surface and to an appropriate concentration of RrgA on the AFM cantilever tip, apparent by the target value of up to 20% of interaction events during SMFS measurements and revealed that RrgA binds to Fn with a mean force of 52 pN. The protocol can be adjusted to couple via site specific free thiol groups. This results in a predefined protein or molecule orientation and is suitable for other biophysical applications besides the SMFS.

This protocol describes the covalent immobilization of proteins with a heterobifunctional silane coupling agent to silicon-oxide surfaces designed for the atomic force microscopy based single molecule force spectroscopy which is exemplified by the interaction of RrgA (pilus-1 tip adhesin of S. pneumoniae) with fibronectin.

In recent years, atomic force microscopy (AFM) based single molecule force spectroscopy (SMFS) extended our understanding of molecular properties and ...

Real-time Observation of the DNA Strand Exchange Reaction Mediated by Rad51

The DNA strand exchange reaction mediated by Rad51 is a critical step of homologous recombination. In this reaction, Rad51 forms a nucleoprotein filament on single-stranded DNA (ssDNA) and captures double-stranded DNA (dsDNA) non-specifically to interrogate it for a homologous sequence. After encountering homology, Rad51 catalyzes DNA strand exchange to mediate pairing of the ssDNA with the complementary strand of the dsDNA. This reaction is highly regulated by numerous accessary proteins in vivo. Although conventional biochemical assays have been successfully employed to examine the role of such accessory protein in vitro, kinetic analysis of intermediate formation and its progression into a final product has proven challenging due to the unstable and transient nature of the reaction intermediates. To observe these reaction steps directly in solution, fluorescence resonance energy transfer (FRET)-based real-time observation systems of this reaction were established. Kinetic analysis of real-time observations shows that the DNA strand exchange reaction mediated by Rad51 obeys a three-step reaction model involving the formation of a three-strand DNA intermediate, maturation of this intermediate, and the release of ssDNA from the mature intermediate. The Swi5-Sfr1 complex, an accessary protein conserved in eukaryotes, strongly enhances the second and third steps of this reaction. The FRET-based assays presented here enable us to uncover the molecular mechanisms through which recombination accessary proteins stimulate the DNA strand exchange activity of Rad51. The primary goal of this protocol is to enhance the repertoire of techniques available to researchers in the field of homologous recombination, particularly those working with proteins from species other than Schizosaccharomyces pombe, so that the evolutionary conservation of the findings presented herein can be determined.

Fluorescence resonance energy transfer-based real-time observation systems of the DNA strand exchange reaction mediated by Rad51 were developed. Using the protocols presented here, we are able to detect the formation of reaction intermediates and their conversion into products, while also analyzing the enzymatic kinetics of the reaction.

The DNA strand exchange reaction mediated by Rad51 is a critical step of homologous recombination. In this reaction, Rad51 forms a nucleoprotein filament ...

Real-Time, Semi-Automated Fluorescent Measurement of the Airway Surface Liquid pH of Primary Human Airway Epithelial Cells

In recent years, the importance of mucosal surface pH in the airways has been highlighted by its ability to regulate airway surface liquid (ASL) hydration, mucus viscosity and activity of antimicrobial peptides, key parameters involved in innate defense of the lungs. This is of primary relevance in the field of chronic respiratory diseases such as cystic fibrosis (CF) where these parameters are dysregulated. While different groups have studied ASL pH both in vivo and in vitro, their methods report a relatively wide range of ASL pH values and even contradictory findings regarding any pH differences between non-CF and CF cells. Furthermore, their protocols do not always provide enough details in order to ensure reproducibility, most are low throughput and require expensive equipment or specialized knowledge to implement, making them difficult to establish in most labs. Here we describe a semi-automated fluorescent plate reader assay that enables the real-time measurement of ASL pH under thin film conditions that more closely resemble the in vivo situation. This technique allows for stable measurements for many hours from multiple airway cultures simultaneously and, importantly, dynamic changes in ASL pH in response to agonists and inhibitors can be monitored. To achieve this, the ASL of fully differentiated primary human airway epithelial cells (hAECs) are stained overnight with a pH-sensitive dye in order to allow for the reabsorption of the excess fluid to ensure thin film conditions. After fluorescence is monitored in the presence or absence of agonists, pH calibration is performed in situ to correct for volume and dye concentration. The method described provides the required controls to make stable and reproducible ASL pH measurements, which ultimately could be used as a drug discovery platform for personalized medicine, as well as adapted to other epithelial tissues and experimental conditions, such as inflammatory and/or host-pathogen models.

We present a protocol to make dynamic measurements of the airway surface liquid pH under thin film conditions using a plate-reader.

In recent years, the importance of mucosal surface pH in the airways has been highlighted by its ability to regulate airway surface liquid (ASL) ...

Characterizing Cellular Proteins with In-cell Fast Photochemical Oxidation of Proteins

Fast photochemical oxidation of proteins (FPOP) is a hydroxyl radical protein footprinting method used to characterize protein structure and interactions. FPOP uses a 248 nm excimer laser to photolyze hydrogen peroxide producing hydroxyl radicals. These radicals oxidatively modify solvent exposed side chains of 19 of the 20 amino acids. Recently, this method has been used in live cells (IC-FPOP) to study protein interactions in their native environment. The study of proteins in cells accounts for intermolecular crowding and various protein interactions that are disrupted for in vitro studies. A custom single cell flow system was designed to reduce cell aggregation and clogging during IC-FPOP. This flow system focuses the cells past the excimer laser individually, thus ensuring consistent irradiation. By comparing the extent of oxidation produced from FPOP to the protein&#39;s solvent accessibility calculated from a crystal structure, IC-FPOP can accurately probe the solvent accessible side chains of proteins.

Here, we characterize protein structure and interaction sites in living cells using a protein footprinting technique termed in-cell fast photochemical oxidation of proteins (IC-FPOP).

Fast photochemical oxidation of proteins (FPOP) is a hydroxyl radical protein footprinting method used to characterize protein structure and interactions. ...

Acyl-PEGyl Exchange Gel Shift Assay for Quantitative Determination of Palmitoylation of Brain Membrane Proteins

Activity-dependent alterations in the levels of synaptic AMPA receptors (AMPARs) within the postsynaptic density (PSD) is thought to represent a cellular mechanism for learning and memory. Palmitoylation regulates localization and function of many synaptic proteins including AMPA-Rs, auxiliary factors and synaptic scaffolds in an activity-dependent manner. We identified the synapse differentiation induced gene (SynDIG) family of four genes (SynDIG1-4) encoding brain-specific transmembrane proteins that associate with AMPARs and regulate synapse strength. SynDIG1 is palmitoylated at two cysteine residues located at positions 191 and 192 in the juxta-transmembrane region important for activity-dependent excitatory synapse development. Here, we describe an innovative biochemical approach, the acyl-PEGyl exchange gel shift (APEGS) assay, to investigate the palmitoylation state of any protein of interest and demonstrate its utility with the SynDIG family of proteins in mouse brain lysates.

Palmitoylation entails the incorporation of a 16-carbon palmitate moiety to cysteine residues of target proteins in a reversible manner. Here, we describe a biochemical approach, the acyl-PEGyl exchange gel shift (APEGS) assay, to investigate the palmitoylation state of any protein of interest in mouse brain lysates.

Activity-dependent alterations in the levels of synaptic AMPA receptors (AMPARs) within the postsynaptic density (PSD) is thought to represent a cellular ...

Measuring Nucleotide Binding to Intact, Functional Membrane Proteins in Real Time

We have developed a method to measure binding of adenine nucleotides to intact, functional transmembrane receptors in a cellular or membrane environment. This method combines expression of proteins tagged with the fluorescent non-canonical amino acid ANAP, and FRET between ANAP and fluorescent (trinitrophenyl) nucleotide derivatives. We present examples of nucleotide binding to ANAP-tagged KATP ion channels measured in unroofed plasma membranes and excised, inside-out membrane patches under voltage clamp. The latter allows for simultaneous measurements of ligand binding and channel current, a direct readout of protein function. Data treatment and analysis are discussed extensively, along with potential pitfalls and artefacts. This method provides rich mechanistic insights into the ligand-dependent gating of KATP channels and can readily be adapted to the study of other nucleotide-regulated proteins or any receptor for which a suitable fluorescent ligand can be identified.

This protocol presents a method for measuring adenine nucleotide binding to receptors in real time in a cellular environment. Binding is measured as F&#246;rster resonance energy transfer (FRET) between trinitrophenyl nucleotide derivatives and protein labeled with a non-canonical, fluorescent amino acid.

We have developed a method to measure binding of adenine nucleotides to intact, functional transmembrane receptors in a cellular or membrane environment. ...

Transverse Sectioning of Mature Rice (Oryza sativa L.) Kernels for Scanning Electron Microscopy Imaging Using Pipette Tips as Immobilization Support

Starch granules (SGs) exhibit different morphologies depending on the plant species, especially in the endosperm of the Poaceae family. Endosperm phenotyping can be used to classify genotypes based on SG morphotype using scanning electron microscopic (SEM) analysis. SGs can be visualized using SEM by slicing through the kernel (pericarp, aleurone layers, and endosperm) and exposing the organellar contents. Current methods require the rice kernel to be embedded in plastic resin and sectioned using a microtome or embedded in a truncated pipette tip and sectioned by hand using a razor blade. The former method requires specialized equipment and is time-consuming, while the latter introduces a new host of problems depending on rice genotype. Chalky rice varieties, particularly, pose a problem for this type of sectioning due to the friable nature of their endosperm tissue. Presented here is a technique for preparing translucent and chalky rice kernel sections for microscopy, requiring only pipette tips and a scalpel blade. Preparing the sections within the confines of a pipette tip prevents rice kernel endosperm from shattering (for translucent or &#8216;vitreous&#8217; phenotypes) and crumbling (for chalky phenotypes). Using this technique, endosperm cell patterning and the structure of intact SGs can be observed.

Transverse Sectioning of Mature Rice Oryza sativa L. Kernels for Scanning Electron Microscopy Imaging Using Pipette Tips as Immobilization Support

This protocol allows for the preparation of transverse sections of cereal seeds (e.g., rice) for the analysis of endosperm and starch granule morphology using scanning electron microscopy.