Name: identifying amino acid overproducers using rare-codon-rich markers
Uploaded: 2019-06-24T13:30:00
Description: Watch this Scientific Journal Video about Identifying Amino Acid Overproducers Using Rare-Codon-Rich Markers at JoVE.com

The work was jointly supported by the National Natural Science Foundation of China (grant no. 21676026), the National Key R&#38;D Program of China (grant no. 2017YFD0201400), and the China Postdoctoral Science Foundation (grant no. 2017M620643). Works in the UCLA Institute of Advancement (Suzhou) were supported by the internal grants from Jiangsu Province and Suzhou Industrial Park.

1. Construction of the plasmids expressing the rare-codon-rich marker genes
<ol>
	<li>Select a marker gene that contains an appropriate number of the common codons for the targeted amino acid. 
	NOTE: For L-leucine, the kanamycin resistance gene kanR, which contains 29 leucine codons, of which 27 are common codons, is used for the construction of the selection system13. The gfp gene, which contains 17 common codons out of 19 leucine codons, or the purple protein...

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The number of rare codons in the marker genes and the selection or screening medium are critical to inhibit protein expressions from the rare-codon-modified marker genes. If no significant difference can be detected between protein expressions from the wild-type marker genes and their derivatives, increasing the number of rare codons or using a nutrient-limited medium may amplify the differences. However, if the inhibition effect is too strong, the protein expressions may not be recovered even by extra feeding of the cor...

The current production of amino acids relies heavily on fermentation. However, the titers and yields for most amino acid production strains are below the rising demands of the global amino acid market that is worth billions of dollars1,2. Obtaining high-performance amino acid overproducers are critical for the upgrade of the amino acid industry.
Traditional strategy to identify amino acid overproducers exploits the competitions between amino acids and their analogs in protein synthesis3,4. These analogs are able to charge the tRNAs that recognize the corresponding amino acids and thus inhibit the elongations of the peptide chains, leading to arrested growth or cell death5. One way to resist the analog stresses is to increase the concentrations of intracellular amino acids. The enriched amino acids will outcompete the analogs for the finite tRNAs and ensure the correct synthesis of functional proteins. Therefore, strains that survive the analogs can be selected and are likely the overproducers of the corresponding amino acids.
Although proved successful in selecting overproducers for amino acids such as L-leucine6, the analog-based strategy suffers from severe drawbacks. One major concern is the analog resistance originated from the process of mutagenesis or through spontaneous mutations. Strains with resistance can escape the selection by blocking, exporting, or degrading the analogs5. Another concern is the toxic side effects of the analogs on other cellular processes7. As a consequence, strains that survive the analog selection may not be the amino acid overproducers, while the desired overproducers could be falsely exterminated due to the negative side effects.
Here, a novel strategy based on the law of codon bias is presented in order to achieve accurate and rapid identifications of amino acid overproducers. Most amino acids are encoded by more than one nucleotide&#160;triplet that is favored differently by the host organisms8,9. Some codons are rarely used in the coding sequences and are referred to as the rare codons. Their translations into amino acids rely on the cognate tRNAs that carry the corresponding amino acids. However, the tRNAs that recognize rare codons usually have much lower abundances than the tRNAs of the common codons10,11. Consequently, these rare tRNAs are less likely to capture the free amino acids in the competitions with other isoacceptors, and translations of the rare-codon-rich sequences begin to decelerate or even are terminated when the amounts of amino acids are limited10. The translations could, theoretically, be restored if there is an amino acid surplus after charging the synonymous common tRNAs due to overproductions or extra feedings of the corresponding amino acids12. If the rare-codon-rich gene encodes a selection or screening marker, strains exhibiting the corresponding phenotypes can then be readily identified and are likely the overproducers of the targeted amino acids.
The above strategy is applied to establish a selection and a screening system for the identification of amino acid overproducers. The selection system uses antibiotic resistance genes (e.g., kanR) as markers while the screening system uses the genes encoding fluorescent (e.g., green fluorescent protein [GFP]) or chromogenic (e.g., PrancerPurple) proteins. The marker genes in both systems are modified by replacing defined numbers of the common codons for the targeted amino acid with its synonymous rare alternative. Strains in the mutation library that harbor the rare-codon-rich marker gene are selected or screened under proper conditions, and the overproducers of the targeted amino acids can be readily identified. The workflow begins with the construction of the rare-codon-rich marker gene system, followed by the optimization of the working conditions, and then the identification and verification of the amino acid overproducers. This analog-independent strategy is based on the dogma in protein translation and has been practically verified to enable accurate and rapid identifications of amino acid overproducers. Theoretically, it could be directly employed to amino acids with rare codons and to all microorganisms. In all, the rare-codon-based strategy will serve as an efficient alternative to the conventional analog-based approach when proper analogs for specific amino acids are unavailable, or when a high false positive rate is the major concern. The protocol below uses leucine rare codon to demonstrate this strategy in identifying Escherichia coli L-leucine overproducers.

<table>
	<tbody>
		<tr>
			<td>Acetonitrile</td>
			<td>Thermo</td>
			<td>51101</td>
			<td></td>
		</tr>
		<tr>
			<td>EasyPure HiPure Plasmid MiniPrep Kit</td>
			<td>Transgen</td>
			<td>EM111-01</td>
			<td></td>
		</tr>
		<tr>
			<td>EasyPure Quick Gel Extraction Kit</td>
			<td>Transgen</td>
			<td>EG101-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Gibson assembly master mix</td>
			<td>NEB</td>
			<td>E2611S</td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropyl &#946;-D-1-thiogalactopyranoside</td>
			<td>Solarbio</td>
			<td>I8070</td>
			<td></td>
		</tr>
		<tr>
			<td>L-leucine</td>
			<td>Sigma</td>
			<td>L8000</td>
			<td></td>
		</tr>
		<tr>
			<td>Microplate reader</td>
			<td>Biotek</td>
			<td>Synergy 2</td>
			<td></td>
		</tr>
		<tr>
			<td>n-hexane</td>
			<td>Thermo</td>
			<td>H3061</td>
			<td></td>
		</tr>
		<tr>
			<td>Phenyl isothiocyanate</td>
			<td>Sigma</td>
			<td>P1034</td>
			<td></td>
		</tr>
		<tr>
			<td>PrancerPurple CPB-37-441</td>
			<td>ATUM</td>
			<td>CPB-37-441</td>
			<td></td>
		</tr>
		<tr>
			<td>TransStar FastPfu Fly DNA polymerase</td>
			<td>Transgen</td>
			<td>AP231-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Triethylamine</td>
			<td>Sigma</td>
			<td>T0886</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultra-high performance liquid chromatography</td>
			<td>Agilent</td>
			<td>1290 Infinity II</td>
			<td></td>
		</tr>
		<tr>
			<td>Wild type C. glutamicum</td>
			<td>ATCC</td>
			<td>13032</td>
			<td></td>
		</tr>
		<tr>
			<td>XL10-Gold E. coli competent cell</td>
			<td>Agilent</td>
			<td>200314</td>
			<td></td>
		</tr>
		<tr>
			<td>ZORBAX RRHD Eclipse Plus C18 column</td>
			<td>Agilent</td>
			<td>959759-902K</td>
			<td></td>
		</tr>
	</tbody>
</table>

identifying amino acid overproducers using rare-codon-rich markers

To satisfy the ever-growing market for amino acids, high-performance production strains are needed. The amino acid overproducers are conventionally identified by harnessing the competitions between amino acids and their analogs. However, this analog-based method is of low accuracy, and proper analogs for specific amino acids are limited. Here, we present an alternative strategy that enables an accurate, sensitive, and high-throughput screening of amino acid overproducers using rare-codon-rich markers. This strategy is inspired by the phenomenon of codon usage bias in protein translation, for which codons are categorized into common or rare ones based on their frequencies of occurrence in the coding DNA. The translation of rare codons depends on their corresponding rare transfer RNAs (tRNAs), which cannot be fully charged by the cognate amino acids under starvation. Theoretically, the rare tRNAs can be charged if there is a surplus of the amino acids after charging the synonymous common isoacceptors. Therefore, retarded translations caused by rare codons could be restored by feeding or intracellular overproductions of the corresponding amino acids. Under this assumption, a selection or screening system for identifying amino acid overproducers is established by replacing the common codons of the targeted amino acids with their synonymous rare alternatives in the antibiotic resistance genes or the genes encoding fluorescent or chromogenic proteins. We show that the protein expressions can be greatly hindered by the incorporation of rare codons and that the levels of proteins correlate positively with the amino acid concentrations. Using this system, overproducers of multiple amino acids can be readily screened out from mutation libraries. This rare-codon-based strategy only requires a single modified gene, and the host is less likely to escape the selection than in other methods. It offers an alternative approach for obtaining amino acid overproducers.

For the selection system, a sharp decrease in OD600 for strains harboring the rare-codon-rich antibiotic resistance gene should be observed in comparison to the strain harboring the wild-type antibiotic resistance gene when cultured in a suitable medium (Figure 1a). Under the same conditions, the decrease in cell OD600 becomes more obvious as the number of rare codons in the antibiotic resistance gene increases (Figu...

Watch this Scientific Journal Video about Identifying Amino Acid Overproducers Using Rare-Codon-Rich Markers at JoVE.com

Identifying Amino Acid Overproducers Using Rare-Codon-Rich Markers

This study presents an alternative strategy to the conventional toxic analog-based method in identifying amino acid overproducers by using rare-codon-rich markers to achieve accuracy, sensitivity, and high-throughput simultaneously.

To satisfy the ever-growing market for amino acids, high-performance production strains are needed. The amino acid overproducers are conventionally ...

This method provides an efficient alternative to the conventional analog-based approach in obtaining amino acid overproducers. This technique outcompetes the traditional analog-based method by providing accuracy, sensitivity, and high throughput simultaneously. This method sheds new light on understanding amino acid overproduction strengths and the translation of rare codons and could, theoretically, be applied to all microorganisms.This protocol relies mostly on basic molecular experimental operations which are easy to follow but may require multiple trials in order to achieve the suitable selection of straining stringencies. A visual demonstration of this technique offers a direct appreciation on the performance of the selection and a screening system in identifying amino acid producers. To begin this procedure, add the vector in the marker fragments, on ice, in a molar ratio of one to one to seven point five microliters of assembly mix to a total volume of ten microliters.Incubate at 50 degrees Celsius for one hour. Transform five microliters of the assembly product into 50 microliters of component cells at 42 degrees Celsius for 30 seconds. Recover the cells in Super Optimal broth with Catabolite repression medium at 37 degrees Celsius for one hour.Then, plate them on LB Agar medium and incubate overnight at 37 degrees Celsius. The next day, use a preferred commercial kit to isolate the plasmid. First, transform 50 microliters of the competent cells with one microliter of plasmid that carries the wild-type KanR.Transform a second set of the competent cells with the plasmid containing KanR RC 29 with all leucine codons replaced by the rare codon CTA. Plate and incubate the cell culture as outlined in the text protocol. Next, transfer the colonies that harbor the wild-type selection marker gene in the rare-codon-rich derivative individually into five milliliters of five-fold diluted LB medium containing kanamycin at a concentration of 50 micrograms per milliliter.Incubate the samples in a shaker at 37 degrees Celsius while shaking at 250 rpm. Then, transfer 200 microliters of each of the cell cultures into a 96 well plate in triplicate at defined time points. Use a plate reader to measure the OD600.Inoculate the stains harboring the KanR RC 29 marker gene in two sets of five milliliters of the 0.2 x LB medium that contains kanamycin, with or without a supply of L-leucine. Add L-leucine to one of the media to a final concentration of one gram per liter. Incubate the samples in a shaker at 37 degrees Celsius with shaking at 250 rpm and measure the OD600 for each culture at defined time points.To begin, transform 50 microliters of the parent strain used for mutagenesis with one microliter of plasmid that carries the wild-type GFP or the wild-type PPG. Plate and incubate the cell cultures as outlined in the text protocol. Next, transfer the colonies individually to five milliliters of the properly diluted LB medium.Incubate the samples in a shaker at 37 degrees Celsius with shaking at 250 rpm. For fluorescence markers, transfer 200 microliters of the cell cultures into a 96 well clear bottom back plate in triplicate at defined time points. Measure the OD600 in the fluorescence and calculate the fluorescence intensity.For chromogenic markers, measure the color development of the cell cultures. Perform the feeding assay as previously described and measure the fluorescence intensity or the color development at defined time points. First, transform 50 microliters of the mutant cells with one microliter of the plasmid carrying the selection marker KanR RC 29, or the screening markers GFP RC or PPG RC.Next, centrifuge the cell cultures at 4000 times G for five minutes.For selection, discard the supernatant and add five milliliters of 0.2 x LB medium containing kanamycin to cells carrying the selection marker. Incubate the sample overnight in a shaker at 37 degrees Celsius. The next day, plate the overnight culture onto 0.2 x LB agar medium containing kanamycin and incubate at 37 degrees Celsius for 12 hours.For screening, plate the appropriate number of cells harboring the screening marker onto LB agar medium containing the appropriate antibiotic. Incubate at 37 degrees Celsius for eight hours. After this, inoculate the LB medium containing the appropriate antibiotic with each single colony from the plate.Incubate the samples in a shaker at 37 degrees Celsius while shaking at 250 rpm. Measure the OD600 and the fluorescence and calculate the fluorescence intensity if GFP RC is used. Measure the color development of the cell cultures if PPG RC is used.To verify the amino acid productivities of the candidate strains, prepare seed culture by inoculating five milliliters of LB medium with each of the candidate strains and let the cells grow overnight in a shaker at 250 rpm and at 37 degrees Celsius. The next day, harvest the cells from one milliliter of the cell culture by centrifuging at 4000 times G for two minutes. Discard the supernatant and resuspend the palette with one milliliter of sterile water.Inoculate 20 milliliters of M9 medium containing four percent glucose with 200 microliters of the cell suspension and incubate in a 250 milliliter shaker at 250 rpm and at 37 degrees Celsius for 24 hours. The next day, centrifuge one milliliter of the culture medium at 4000 times G for five minutes. Transfer 200 microliters of the supernatant into a clean 1.5 milliliter tube.Prepare L-leucine standard solutions at the concentrations shown here. In a fume hood, add 100 microliters of one millimolar triethylamine and 100 microliters of one molar phenyl isothiocyanate to both the supernatant and the standards. Mix the solutions gently and incubate them at room temperature for one hour.Then, add 400 microliters of n-hexane to the same tube and vortex it for ten seconds. The lower phase contains the amino acid derivatives and is used for HPLC analysis. Filter the lower phase through 0.2 microliter polytetrafluoroethylene membranes.After this, run one microliter of the sample on an ultra HPLC equipped with a C18 column with a flow rate of 0.42 milliliters per minute and at column temperature for 40 degrees Celsius. Use a diode array detector to detect the targeted amino acids at 254 nanometers and calculate their concentrations by mapping the peak areas under the standard curve. In this study, amino acid overproducers are identified by using rare codon-rich markers to simultaneously achieve accuracy, sensitivity, and high-throughput.For the selection system, a sharp decrease in OD600 for strains harboring the rare codon-rich antibiotic resistance gene should be observed in comparison to the strain harboring the wild-type. The inhibition of rare codon on protein expressions mostly takes place under starved conditions. After extra feeding of the corresponding amino acid, the OD600 for the strain harboring the rare codon-rich antibiotic resistance gene increases significantly.For the screening system, the fluorescence intensity in the number of fluorescent cells are significantly lower for the strain that expresses the fluorescent protein from the rare codon-rich gene than from the wild-type gene. Feeding of the corresponding amino acid will restore protein expressions from the rare codon-rich genes. When using the purple protein, the color developed from the rare codon-rich PPG is lighter than that from the wild-type gene.The undiluted LB medium allows slow expression of the rare codon-rich PPG without L-leucine feeding in the expressed purple protein becomes visible once the cells are pelleted. However, this does not conceal the fact that gene expression from the rare codon-rich PPG is enhanced by feeding of the L-leucine. The rare codon-based strategy could identify overproducers of the targeted amino acids from the mutation library and these mutants should produce higher amounts of the targeted amino acids than the parent strains.When attempting this procedure, it is important to adjust rare codon frequency to achieve a clear discrimination in the OD or color between cells harboring the wild-type markers and the rare codon-rich derivatives. Transcriptome analysis and the genome sequencing could be applied to the selected strains to investigate the mechanism related to amino acid productions. Using this technique, amino acid overproducers could be efficiently identified and analysis of their genetic information would offer new insights into their mechanisms behind amino acid overproductions.Amino acid derivatization could be harmful. Make sure to wear gloves and the protective clothing and perform these steps in a fume hood.

identifying-amino-acid-overproducers-using-rare-codon-rich-markers

Research

JoVE Journal

Biochemistry

Method for Identifying Small Molecule Inhibitors of the Protein-protein Interaction Between HCN1 and TRIP8b

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed ubiquitously throughout the brain, where they function to regulate the excitability of neurons. The subcellular distribution of these channels in pyramidal neurons of hippocampal area CA1 is regulated by tetratricopeptide repeat-containing Rab8b interacting protein (TRIP8b), an auxiliary subunit. Genetic knockout of HCN pore forming subunits or TRIP8b, both lead to an increase in antidepressant-like behavior, suggesting that limiting the function of HCN channels may be useful as a treatment for Major Depressive Disorder (MDD). Despite significant therapeutic interest, HCN channels are also expressed in the heart, where they regulate rhythmicity. To circumvent off-target issues associated with blocking cardiac HCN channels, our lab has recently proposed targeting the protein-protein interaction between HCN and TRIP8b in order to specifically disrupt HCN channel function in the brain. TRIP8b binds to HCN pore forming subunits at two distinct interaction sites, although here the focus is on the interaction between the tetratricopeptide repeat (TPR) domains of TRIP8b and the C terminal tail of HCN1. In this protocol, an expanded description of a method for purifying TRIP8b and executing a high throughput screen to identify small molecule inhibitors of the interaction between HCN and TRIP8b, is described. The method for high throughput screening utilizes a Fluorescence Polarization (FP) -based assay to monitor the binding of a large TRIP8b fragment to a fluorophore-tagged eleven amino acid peptide corresponding to the HCN1 C terminal tail. This method allows &#39;hit&#39; compounds to be identified based on the change in the polarization of emitted light. Validation assays are then performed to ensure that &#39;hit&#39; compounds are not artifactual.

The interaction between HCN channels and their auxiliary subunit has been identified as a therapeutic target in Major Depressive Disorder. Here, a fluorescence polarization-based method for identifying small molecule inhibitors of this protein-protein interaction, is presented.

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed ubiquitously throughout the brain, where they function to regulate the ...

Voltage-clamp Fluorometry in Xenopus Oocytes Using Fluorescent Unnatural Amino Acids

Voltage-Clamp Fluorometry (VCF) has been the technique of choice to investigate the structure and function of electrogenic membrane proteins where real-time measurements of fluorescence and currents simultaneously report on local rearrangements and global function, respectively1. While high-resolution structural techniques such as cryo-electron microscopy or X-ray crystallography provide static images of the proteins of interest, VCF provides dynamic structural data that allows us to link the structural rearrangements (fluorescence) to dynamic functional data (electrophysiology). Until recently, the thiol-reactive chemistry used for site-directed fluorescent labeling of the proteins restricted the scope of the approach because all accessible cysteines, including endogenous ones, will be labeled. It was thus required to construct proteins free of endogenous cysteines. Labeling was also restricted to sites accessible from the extracellular side. This changed with the use of Fluorescent Unnatural Amino Acids (fUAA) to specifically incorporate a small fluorescent probe in response to stop codon suppression using an orthogonal tRNA and tRNA synthetase pair2. The VCF improvement only requires a two-step injection procedure of DNA injection (tRNA/synthetase pair) followed by RNA/fUAA co-injection. Now, labelling both intracellular and buried sites is possible, and the use of VCF has expanded significantly. The VCF technique thereby becomes attractive for studying a wide range of proteins and &#8211; more importantly &#8211; allows investigating numerous cytosolic regulatory mechanisms.

Voltage-clamp Fluorometry in Xenopus Oocytes Using Fluorescent Unnatural Amino Acids

This article describes an enhancement of conventional Voltage-Clamp Fluorometry (VCF) where Fluorescent Unnatural Amino Acids (fUAA) are used instead of maleimide dyes, to probe structural rearrangements in ion channels. The procedure includes Xenopus oocyte DNA injection, RNA/fUAA coinjection, and simultaneous current and fluorescence measurements.

Voltage-Clamp Fluorometry (VCF) has been the technique of choice to investigate the structure and function of electrogenic membrane proteins where ...

Hydrolysis of a Ni-Schiff-Base Complex Using Conditions Suitable for Retention of Acid-labile Protecting Groups

Unnatural amino acids, amino acids containing side-chain functionalities not commonly seen in nature, are increasingly found in synthetic peptide sequences. Synthesis of some unnatural amino acids often includes the use of a precursor consisting of a Schiff-base stabilized by a nickel cation. Unnatural side-chains can be installed on an amino acid backbone found in this Schiff-base complex. The resulting unnatural amino acid can then be isolated from this complex using hydrolysis of the Schiff-base, typically by employing reflux in strongly acidic solution. These highly acidic conditions may remove acid-labile side-chain protecting groups necessary for the unnatural amino acids to be used in microwave-assisted solid-phase peptide synthesis. In this work, we present an efficient hydrolysis and subsequent Fmoc protection of an amino acid isolated from a Ni-Schiff base complex. Hydrolysis conditions presented in this work are suitable for retention of acid-labile side-chain protecting groups and may be adaptable to a variety of unnatural amino acid substrates.

Here, we present an efficient hydrolysis and subsequent Fmoc protection of an amino acid isolated from a Ni-Schiff-base complex. Hydrolysis conditions presented here are suitable for use when retention of acid-labile side-chain protecting groups is required. This technique may be adaptable to a variety of unnatural amino acid substrates.

Unnatural amino acids, amino acids containing side-chain functionalities not commonly seen in nature, are increasingly found in synthetic peptide ...

Kinetic Screening of Nuclease Activity using Nucleic Acid Probes

Nucleases are a class of enzymes that break down nucleic acids by catalyzing the hydrolysis of the phosphodiester bonds that link the ribose sugars. Nucleases display a variety of vital physiological roles in prokaryotic and eukaryotic organisms, ranging from maintaining genome stability to providing protection against pathogens. Altered nuclease activity has been associated with several pathological conditions including bacterial infections and cancer. To this end, nuclease activity has shown great potential to be exploited as a specific biomarker. However, a robust and reproducible screening method based on this activity remains highly desirable.
Herein, we introduce a method that enables screening for nuclease activity using nucleic acid probes as substrates, with the scope of differentiating between pathological and healthy conditions. This method offers the possibility of designing new probe libraries, with increasing specificity, in an iterative manner. Thus, multiple rounds of screening are necessary to refine the probes&#39; design with enhanced features, taking advantage of the availability of chemically modified nucleic acids. The considerable potential of the proposed technology lies in its flexibility, high reproducibility, and versatility for the screening of nuclease activity associated with disease conditions. It is expected that this technology will allow the development of promising diagnostic tools with a great potential in the clinic.

Altered nuclease activity has been associated with different human conditions, underlying its potential as a biomarker. The modular and easy to implement screening methodology presented in this paper allows the selection of specific nucleic acid probes for harnessing nuclease activity as a biomarker of disease.

Nucleases are a class of enzymes that break down nucleic acids by catalyzing the hydrolysis of the phosphodiester bonds that link the ribose sugars. ...

Isolation of Histone from Sorghum Leaf Tissue for Top Down Mass Spectrometry Profiling of Potential Epigenetic Markers

Histones belong to a family of highly conserved proteins in eukaryotes. They pack DNA into nucleosomes as functional units of chromatin. Post-translational modifications (PTMs) of histones, which are highly dynamic and can be added or removed by enzymes, play critical roles in regulating gene expression. In plants, epigenetic factors, including histone PTMs, are related to their adaptive responses to the environment. Understanding the molecular mechanisms of epigenetic control can bring unprecedented opportunities for innovative bioengineering solutions. Herein, we describe a protocol to isolate the nuclei and purify histones from sorghum leaf tissue. The extracted histones can be analyzed in their intact forms by top-down mass spectrometry (MS) coupled with online reversed-phase (RP) liquid chromatography (LC). Combinations and stoichiometry of multiple PTMs on the same histone proteoform can be readily identified. In addition, histone tail clipping can be detected using the top-down LC-MS workflow, thus, yielding the global PTM profile of core histones (H4, H2A, H2B, H3). We have applied this protocol previously to profile histone PTMs from sorghum leaf tissue collected from a large-scale field study, aimed at identifying epigenetic markers of drought resistance. The protocol could potentially be adapted and optimized for chromatin immunoprecipitation-sequencing (ChIP-seq), or for studying histone PTMs in similar plants.

The protocol has been developed to effectively extract intact histones from sorghum leaf materials for profiling of histone post-translational modifications that can serve as potential epigenetic markers to aid engineering drought resistant crops.

Histones belong to a family of highly conserved proteins in eukaryotes. They pack DNA into nucleosomes as functional units of chromatin. ...

Estimation of Plant Biomass Lignin Content using Thioglycolic Acid (TGA)

Lignin is a natural polymer that is the second most abundant polymer on Earth after cellulose. Lignin is mainly deposited in plant secondary cell walls and is an aromatic heteropolymer primarily composed of three monolignols with significant industrial importance. Lignin plays an important role in plant growth and development, protects&#160;from biotic and abiotic stresses, and in the quality of animal fodder, the wood, and industrial lignin products. Accurate estimation of lignin content is essential for both fundamental understanding of the lignin biosynthesis and industrial applications of biomass. The thioglycolic acid (TGA) method is a highly reliable method of estimating the total lignin content in the plant biomass. This method estimates the lignin content by forming thioethers with the benzyl alcohol groups of lignin, which are soluble in alkaline conditions and insoluble in acidic conditions. The total lignin content is estimated using a standard curve generated from commercial bamboo lignin.

Estimation of Plant Biomass Lignin Content using Thioglycolic Acid TGA

Here, we present a modified TGA method for estimation of lignin content in herbaceous plant biomass. This method estimates the lignin content by forming specific thioether bonds with lignin and presents an advantage over the Klason method, as it requires a relatively small sample for lignin content estimation.

Lignin is a natural polymer that is the second most abundant polymer on Earth after cellulose. Lignin is mainly deposited in plant secondary cell walls ...

Optimized Incorporation of Alkynyl Fatty Acid Analogs for the Detection of Fatty Acylated Proteins using Click Chemistry

Fatty acylation, the covalent addition of saturated fatty acids to protein substrates, is important in regulating a myriad of cellular functions in addition to its implications in cancer and neurodegenerative diseases. Recent developments in fatty acylation detection methods have enabled efficient and non-hazardous detection of fatty acylated proteins, particularly through the use of click chemistry with bio-orthogonal labeling. However, click chemistry detection can be limited by the poor solubility and potential toxic effects of adding long chain fatty acids to cell culture. Described here is a labeling approach with optimized delivery using saponified fatty acids in combination with fatty-acid free BSA, as well as delipidated media, which can improve detection of hard to detect fatty acylated proteins. This effect was most pronounced with the alkynyl-stearate analog, 17-ODYA, which has been the most commonly used fatty acid analog in click chemistry detection of acylated proteins. This modification will improve cellular incorporation and increase sensitivity to acylated protein detection. In addition, this approach can be applied in a variety of cell types and combined with other assays such as pulse-chase analysis, stable isotope labeling with amino acids in cell culture, and mass spectrometry for quantitative profiling of fatty acylated proteins.

The study of fatty acylation has important implications in cellular protein interactions and diseases. Presented here is a modified protocol to improve click chemistry detection of fatty acylated proteins, which can be applied in various cell types and combined with other assays, including pulse-chase and mass spectrometry.

Fatty acylation, the covalent addition of saturated fatty acids to protein substrates, is important in regulating a myriad of cellular functions in ...

Folding and Probing of Nucleic Acid Constructs

Begin by pipetting G4-TBA, single-stranded TBA, and double-stranded TBA solutions into three different tubes for folding. Heat the samples to 95 degrees Celsius for five minutes. Let them cool slowly to room temperature.Once the tubes have cooled to room temperature, centrifuge the tubes. Next, organize three sets each of seven empty autoclaved 0.5-milliliter tubes. Add three microliters of ultrapure water into each tube.Pipette five microliters of the folded nucleic acid constructs into each tube of the set. Next, add two microliters of either 25 or 250-micromolar B-CEP1 to obtain the final probe concentration of five and 50 micromolar respectively. To the three control tubes, add ultrapure water instead of the compound and incubate all the samples at 37 degrees Celsius.Stop the reaction by placing the tubes at 20 degrees Celsius, then dry the samples in a vacuum centrifuge.

Separation of Polymerized Nucleic Acid Constructs by PAGE 

Begin by preparing a polymerized page gel sandwich. Remove the clamps and paper tape layers, and slowly remove the comb. Thoroughly rinse the wells with distilled water.Place the gel sandwich correctly in the vertical electrophoresis apparatus. Fill the top and bottom reservoirs with TBE buffer. Warm up the plates by performing a pre-run of the gel electrophoresis for at least 30 minutes at 50 watts.Meanwhile, re-suspend the dried samples in five microliters of denaturing gel loading buffer. Next, use a small syringe filled with TBE buffer to flush the urea out of the wells of the gel. Now load the samples into the clean wells, taking note of the odor of loading.Run the gel for two hours at 50 watts or until the bromophenol blue dye has run down 2/3 of the gel. After electrophoresis, turn off the power supply, carefully remove the glass sandwich, and clean the glass plates. Place the gel in a gel imager to detect the fluorescence of the FAM-labeled oligonucleotide bands.After one, four, and 15 hours of incubation, either five or 50 Micromolar Bsep 1 reacted with two micromolar samples of G4 TBA, single-stranded TBA, and double-stranded TBA. Controls were loaded for each set of samples. The G4 TBA substrate showed only one alkylation adduct due to the availability of only G8 for alkylation and subsequent stranded cleavage.Multiple adducts and bands of cleavage products were observed in single and double-stranded TBA, because all guanines were susceptible to Bsep reaction. Probing reaction and tris buffer resulted in inefficient chemical mapping due to the presence of undesired nucleophiles, causing reduced proprioactivity. The G4 TBA samples showed only the formation of adduct without stranded cleavage.For the single and double-stranded TBA, only a 24-hour incubation led to DNA fragmentation, comparable to the 15-hour fragmentation without Tris.

Predicting Amino Acid Preferences of Protein-Protein Binding Interfaces

Computational Prediction of Amino Acid Preferences of Potentially Multispecific Peptide-Binding Domains Involved in Protein-Protein Interactions

Many protein-protein interactions involve the binding of short protein segments to peptide-binding domains. Usually, such interactions require the recognition of linear motifs with variable conservation. The combination of highly conserved and more variable regions in the same ligands often contributes to the multispecificity of binding, a common property of enzymes and cell signaling proteins. Characterization of amino acid preferences of peptide-binding domains is important for the design of mediators of protein-protein interactions (PPIs). Computational methods are an efficient alternative to the often costly and cumbersome experimental techniques, enabling the design of potential mediators that can be later validated in downstream experiments. Here, we described a methodology using the Pepspec application of the Rosetta molecular modeling package to predict the amino acid preferences of peptide-binding domains. This methodology is useful when the structure of the receptor protein and the nature of the peptide ligand are both known or can be inferred. The methodology starts with a well-characterized anchor from the ligand, which is extended by randomly adding amino acid residues. The binding affinity of peptides generated this way is then evaluated by flexible-backbone peptide docking in order to select the peptides with the best predicted binding scores. These peptides are then used to calculate amino acid preferences and to optionally compute a position-weight matrix (PWM) that can be used in further studies. To illustrate the application of this methodology, we used the interaction between subunits of human interferon regulatory factor 5 (IRF5), previously known to be multispecific but globally guided by a short conserved motif called pLxIS. The estimated amino acid preferences were consistent with previous knowledge about the IRF5 binding surface. Positions occupied by phosphorylatable serine residues exhibited a high frequency of aspartate and glutamate, likely because their negatively charged side chains are similar to phosphoserine.

Author Spotlight: A Computational Approach to Decipher Amino Acid Preferences in Multispecific Protein-Protein Interactions

We describe a methodology based on sequence diversification to estimate the amino acid preferences of multispecific binding sites in protein-protein interactions (PPIs). In this strategy, thousands of potential peptide ligands are generated and screened in silico, thus overcoming some limitations of available experimental methods.