Application to plant proteins of gel electrophoretic methods

A comparative method for protein extraction and 2-D gel electrophoresis from different tissues of Cajanus cajan

Pigeonpea is an important legume crop with high protein content. However, it is often subjected to various abiotic and biotic stresses. Proteomics is a state-of-the-art technique used to analyze the protein profiling of a tissue for deciphering the molecular entities that could be manipulated for developing crops resistant to these stresses. In this context, developing a comprehensive proteome profile from different vegetative and reproductive tissues has become mandatory. Although several protein extraction protocols from different tissues of diverse plant species have been reported, there is no report for pigeonpea. Here, we report tissue-specific protein extraction protocols representing vegetative (young leaves), and reproductive (flowers and seeds) organs and their subsequent analysis on 2-dimensional gel electrophoresis. The study explicitly demonstrated that the efficacy of a particular protein extraction protocol is dependent on the different tissues, such as leaves, flowers and seeds that differ in their structure and metabolic constituents. For instance, phenol-based protocol showed an efficacy toward higher protein yield, better spot resolution and a minimal streaking on 2-DE gel for both leaves and flowers. Protein extraction from seeds was best achieved by employing phosphate-TCA-acetone protocol.

Routine identity confirmation of recombinant proteins by MALDI-TOF mass spectrometry

Peptide mass fingerprinting (PMF) by matrix-assisted laser-desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) provides a simple and direct means to unequivocally confirm identity of recombinant proteins based on predicted peptide profiles. Many universities or research institutions now carry mass spectrometry instrumentation as part of their core bioanalytical facilities or provide public service to outside investigators. This chapter provides methods we have used to generate routinely high quality samples for MALDI-TOF MS analysis. Following resolution of protein preparations by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), we easily process sets of 12 samples manually for MS analysis. Target bands are alkylated and digested in-gel with trypsin, followed by extraction of peptides and desalting with a C18 adsorbent resin (e.g., a "ZipTips"). Acquisition of PMF data on MALDI-TOF mass spectrometers is fast, and with on-site instrumentation, the entire process can be completed within 2 days.

Companion protease inhibitors to protect recombinant proteins in transgenic plant extracts

We describe a general approach for the use of recombinant protease inhibitors as stabilizing agents for clinically useful proteins extracted from transgenic plant tissues. A procedure is first described to assess the overall (in)stability of heterologous proteins in transgenic plant crude protein extracts. Step-by-step protocols are then presented for the choice and use of companion protease inhibitors inhibiting the host plant proteases during extraction. This strategy, that reproduces the protein-stabilizing effect of low-molecular-weight protease inhibitors often added to protein extraction media, does not require the exogenous addition of such expensive and often toxic compounds. It also presents the advantage of being intrinsically scalable to the amount of biomass processed.

Preventing unintended proteolysis in plant protein biofactories

Numerous reports have been published over the last decade assessing the potential of plants as useful hosts for the heterologous expression of clinically useful proteins. Significant progress has been made, in particular, in optimizing transgene transcription and translation in plants, and in elucidating the complex post-translational modifications of proteins typical of the plant cell machinery. In this article, we address the important issue of recombinant protein degradation in plant expression platforms, which directly impacts on the final yield, homogeneity and overall quality of the resulting protein product. Unlike several more stable and structurally less complex pharmaceuticals, recombinant proteins present a natural tendency to structural heterogeneity, resulting in part from the inherent instability of polypeptide chains expressed in heterologous environments. Proteolytic processing, notably, may dramatically alter the structural integrity and overall accumulation of recombinant proteins in plant expression systems, both in planta during expression and ex planta after extraction. In this article, we describe the current strategies proposed to minimize protein hydrolysis in plant protein factories, including organ-specific transgene expression, organelle-specific protein targeting, the grafting of stabilizing protein domains to labile proteins, protein secretion in natural fluids and the co-expression of companion protease inhibitors.

An in-built proteinase inhibitor system for the protection of recombinant proteins recovered from transgenic plants

Proteolytic degradation represents a significant barrier to the efficient production of several recombinant proteins in plants, both in vivo during their expression and in vitro during their recovery from source tissues. Here, we describe a strategy to protect recombinant proteins during the recovery process, based on the coexpression of a heterologous proteinase inhibitor acting as a 'mouse trap' against the host proteases during extraction. After confirming the importance of trypsin- and chymotrypsin-like activities in crude protein extracts of potato (Solanum tuberosum L.) leaves, transgenic lines of potato expressing either tomato cathepsin D inhibitor (CDI) or bovine aprotinin, both active against trypsin and chymotrypsin, were generated by Agrobacterium tumefaciens-mediated genetic transformation. Leaf crude protein extracts from CDI-expressing lines, showing decreased levels of cathepsin D-like and ribulose 1,5-bisphosphate carboxylase/oxygenase hydrolysing activities in vitro, conducted decreased turnover rates of the selection marker protein neomycin phosphotransferase II (NPTII) relative to the turnover rates measured for transgenic lines expressing only the marker protein. A similar stabilizing effect on NPTII was observed in leaf protein extracts from plant lines coexpressing bovine aprotinin, confirming the ability of ectopically expressed broad-spectrum serine proteinase inhibitors to reproduce the protein-stabilizing effect of low-molecular-weight proteinase inhibitors generally added to protein extraction media.

Polymorphism and modulation of cell wall esterase enzyme activities in the chicory root during the growing season

Pectins are major components of the primary plant cell wall. They can be both methylesterified and acetylesterified and de-esterification occurs by specific esterases. Proteins extracted by NaCl treatment from root cell walls of two chicory varieties (Cichorium intybus L. cv. Nausica and Arancha) sampled in an experimental field every 2 weeks between July 2002 and January 2003 were analysed by isoelectrofocalization, semi-denaturing SDS-PAGE, and quantitative assays for their esterase activity. Zymograms showed that chicory root pectin methylesterases belong to a multigene family. The isoelectric points of the pectin methylesterase isoforms ranged from pI 3.8 to pI 9.0. Concerning acetylesterases, only acidic isoforms between pI 4.1 and pI 5.2 were observed, but a large polymorphism of this class of enzymes could be identified in one variety. The results indicate that the root pectin methylesterase activity of the Nausica variety was correlated with ambient temperature, while no significant effect of temperature could be detected on any acetylesterase isoform.

Nod factors induce nod factor cleaving enzymes in pea roots. Genetic and pharmacological approaches indicate different activation mechanisms

Establishment of symbiosis between legumes and rhizobia requires bacterial Nod factors (NFs). The concentration of these lipochitooligosaccharides in the rhizosphere is influenced by plant enzymes. NFs induce on pea (Pisum sativum) a particular extracellular NF hydrolase that releases lipodisaccharides from NFs from Sinorhizobium meliloti. Here, we investigated the ability of non-nodulating pea mutants to respond to NodRlv factors (NFs from Rhizobium leguminosarum bv viciae) with enhanced NF hydrolase activity. Mutants defective in the symbiotic genes sym10, sym8, sym19, and sym9/sym30 did not exhibit any stimulation of the NF hydrolase, indicating that the enzyme is induced via an NF signal transduction pathway that includes calcium spiking (transient increases in intracellular Ca(2+) levels). Interestingly, the NF hydrolase activity in these sym mutants was even lower than in wild-type peas, which were not pretreated with NodRlv factors. Activation of the NF hydrolase in wild-type plants was a specific response to NodRlv factors. The induction of the NF hydrolase was blocked by alpha-amanitin, cycloheximide, tunicamycin, EGTA, U73122, and calyculin A. Inhibitory effects, albeit weaker, were also found for brefeldin A, BHQ and ethephon. In addition to this NF hydrolase, NFs and stress-related signals (ethylene and salicylic acid) stimulated a pea chitinase that released lipotrisaccharides from pentameric NFs from S. meliloti. NodRlv factors failed to stimulate the chitinase in mutants defective in the sym10 and sym8 genes, whereas other mutants (e.g. mutated in the sym19 gene) retained their ability to increase the chitinase activity. These findings indicate that calcium spiking is not implicated in stimulation of the chitinase. We suggest that downstream of Sym8, a stress-related signal transduction pathway branches off from the NF signal transduction pathway.

An electroblotting, two-step procedure for the detection of proteinases and the study of proteinase/inhibitor complexes in gelatin-containing polyacrylamide gels

A two-step gelatin/polyacrylamide gel electrophoresis (gelatin/PAGE) procedure was devised for the detection of proteinases and the study of proteinase/inhibitor interactions in complex biological extracts. The proteins are first resolved by sodium dodecyl sulfate (SDS)-PAGE under reducing or nonreducing conditions, and electrotransferred into a 0.75 mm-thick accompanying polyacrylamide slab gel containing 0.1% w/v porcine gelatin. The active proteinase bands are developed by a gelatin proteolysis step in the accompanying gel in the presence or absence of diagnostic proteinase inhibitors, allowing the assessment of proteinase classes and the visual discrimination of inhibitor-'sensitive' and -'insensitive' proteinases in complex extracts. Alternatively, protein extracts are preincubated with specific reversible inhibitors before electrophoresis, allowing a rapid discrimination of strong and weak interactions implicating proteinases and reversible inhibitors. In comparison with the standard gelatin/PAGE procedure, that involves copolymerization of gelatin with acrylamide in the resolving gel, this new procedure simplifies proteinase patterns, avoids overestimation of proteinase numbers in complex extracts, and allows in certain conditions the estimation of proteinase molecular weights. Stem bromelain (EC 3.4.22.32), bovine trypsin (EC 3.4.21.4), papain (EC 3.4.22.2), and the extracellular (digestive) cysteine proteinases of five herbivorous pests are used as model enzymes to illustrate the usefulness of this approach in detecting proteinases and in studying their interactions with specific proteinaceous inhibitors potentially useful in biotechnology.

Assessing the stability of cystatin/cysteine proteinase complexes using mildly-denaturing gelatin-polyacrylamide gel electrophoresis

A method for assessing the stability of cystatin/cysteine proteinase complexes using mildly-denaturing gelatin-polyacrylamide gel electrophoresis (gelatin-PAGE) is described. As suggested by the use of well-known cystatins (human stefins A and B, and oryzacystatins I and II) and the plant cysteine proteinase papain, the ability of cystatin/cysteine proteinase complexes to remain stable during electrophoresis is associated with the degree of affinity between the enzyme and the inhibitor (and inversely associated with the Ki values), at least with the disulfide bond-lacking cystatins. Complexes with Ki values > or = 10(-8) M (weak interactions) are partly or completely dissociated under the conditions used, while those with lower Ki values (strong interactions) remain stable. As shown by the differential effects of two plant cystatins, oryzacystatins I and II, against a cysteine proteinase present in crude (complex) extracts from a plant pest -- the two-spotted spider mite (Tetranychus urticae Koch), the gelatin-PAGE procedure is suitable for studying the ability of cystatins to form highly stable complexes with cysteine proteinases, without the need for prior purification steps. Considering the well-recognized potential of proteinase inhibitors for pest and pathogen control, this analytical approach will be useful for rapidly assessing the respective potential of various cystatins for protection of plants, animals, and humans.