Modification of recombinant maize ChitA chitinase by fungal chitinase-modifying proteins

Crystal structure of a polyglycine hydrolase determined using a RoseTTAFold model

Polyglycine hydrolases (PGHs) are secreted fungal proteases that cleave the polyglycine linker of Zea mays ChitA, a defensive chitinase, thus overcoming one mechanism of plant resistance to infection. Despite their importance in agriculture, there has been no previous structural characterization of this family of proteases. The objective of this research was to investigate the proteolytic mechanism and other characteristics by structural and biochemical means. Here, the first atomic structure of a polyglycine hydrolase was identified. It was solved by X-ray crystallography using a RoseTTAFold model, taking advantage of recent technical advances in structure prediction. PGHs are composed of two domains: the N- and C-domains. The N-domain is a novel tertiary fold with an as-yet unknown function that is found across all kingdoms of life. The C-domain shares structural similarities with class C β-lactamases, including a common catalytic nucleophilic serine. In addition to insights into the PGH family and its relationship to β-lactamases, the results demonstrate the power of complementing experimental structure determination with new computational techniques.

Functional Characterization of the M36 Metalloprotease FgFly1 in Fusarium graminearum

Fungalysin metallopeptidase (M36), a hydrolase, catalyzes the hydrolysis of alanine, glycine, etc. Normally, it is considered to play an important role in the progress of fungal infection. However, the function of fungalysin metallopeptidase (M36) in Fusarium graminearum has not been reported. In this study, we explored the biological functions of FgFly1, a fungalysin metallopeptidase (M36) of F. graminearum. We found that ΔFgFly1 did not affect the ability to produce DON toxin, although it inhibited spore germination during asexual reproduction and reduction in pathogenicity compared with PH-1. Therefore, we speculated that FgFly1 affects the pathogenicity of F.graminearum by affecting pathways related to wheat disease resistance. Target protein TaCAMTA (calmodulin-binding transcription activator) was selected by a yeast two-hybrid (Y2H) system. Then, the interaction between FgFly1 and TaCAMTA was verified by bimolecular fluorescent complimentary (BiFC) and luciferase complementation assay (LCA). Furthermore, compared with wild-type Arabidopsis thaliana, the morbidity level of ΔAtCAMTA was increased after infection with F.graminearum, and the expression level of NPR1 was significantly reduced. Based on the above results, we concluded that FgFly1 regulated F. graminearum pathogenicity by interacting with host cell CAMTA protein.

Production of selenomethionine labeled polyglycine hydrolases in Pichia pastoris

Producing recombinant proteins with incorporated selenomethionine (SeMet) facilitates solving X-ray crystallographic structures of novel proteins. Production of SeMet labeled proteins in the yeast Pichia pastoris (syn. Komagataella phaffii) is difficult because SeMet is mildly toxic, reducing protein expression levels. To counteract this yield loss for a novel protease, Epicoccum sorghi chitinase modifying protein (Es-cmp), a novel disease promoting protease secreted by these plant pathogenic fungi, we isolated a yeast strain that secreted more protein. By comparing the expression level of 48 strains we isolated one that produced significantly more protein. This strain was found to be gene dosed, having four copies of the expression cassette. After optimization the strain produced Es-cmp in defined media with SeMet at levels nearly equal to that of the original strain in complex media. Also, we produced SeMet labeled protein for a homologous protease from the fungus Fusarium vanettenii, Fvan-cmp, by directly selecting a gene dosed strain on agar plates with increased zeocin. Linearization of plasmid with PmeI before electroporation led to high numbers of 1 mg/mL zeocin resistant clones with significantly increased expression compared to those selected on 0.1 mg/mL. The gene dosed strains expressing Es-cmp and Fvan-cmp allowed production of 8.5 and 16.8 mg of SeMet labeled protein from 500 mL shake flask cultures. The results demonstrate that selection of P. pastoris expression strains by plating after transformation on agar with 1 mg/mL zeocin rather than the standard 0.1 mg/mL directly selects gene dosed strains that can facilitate production of selenomethionine labeled proteins.

Unraveling the sugar code: the role of microbial extracellular glycans in plant-microbe interactions

To defend against microbial invaders but also to establish symbiotic programs, plants need to detect the presence of microbes through the perception of molecular signatures characteristic of a whole class of microbes. Among these molecular signatures, extracellular glycans represent a structurally complex and diverse group of biomolecules that has a pivotal role in the molecular dialog between plants and microbes. Secreted glycans and glycoconjugates such as symbiotic lipochitooligosaccharides or immunosuppressive cyclic β-glucans act as microbial messengers that prepare the ground for host colonization. On the other hand, microbial cell surface glycans are important indicators of microbial presence. They are conserved structures normally exposed and thus accessible for plant hydrolytic enzymes and cell surface receptor proteins. While the immunogenic potential of bacterial cell surface glycoconjugates such as lipopolysaccharides and peptidoglycan has been intensively studied in the past years, perception of cell surface glycans from filamentous microbes such as fungi or oomycetes is still largely unexplored. To date, only few studies have focused on the role of fungal-derived cell surface glycans other than chitin, highlighting a knowledge gap that needs to be addressed. The objective of this review is to give an overview on the biological functions and perception of microbial extracellular glycans, primarily focusing on their recognition and their contribution to plant-microbe interactions.

Use of Dual RNA-seq for Systems Biology Analysis of Zea mays and Aspergillus flavus Interaction

The interaction between Aspergillus flavus and Zea mays is complex, and the identification of plant genes and pathways conferring resistance to the fungus has been challenging. Therefore, the authors undertook a systems biology approach involving dual RNA-seq to determine the simultaneous response from the host and the pathogen. What was dramatically highlighted in the analysis is the uniformity in the development patterns of gene expression of the host and the pathogen during infection. This led to the development of a "stage of infection index" that was subsequently used to categorize the samples before down-stream system biology analysis. Additionally, we were able to ascertain that key maize genes in pathways such as the jasmonate, ethylene and ROS pathways, were up-regulated in the study. The stage of infection index used for the transcriptomic analysis revealed that A. flavus produces a relatively limited number of transcripts during the early stages (0 to 12 h) of infection. At later stages, in A. flavus, transcripts and pathways involved in endosomal transport, aflatoxin production, and carbohydrate metabolism were up-regulated. Multiple WRKY genes targeting the activation of the resistance pathways (i.e., jasmonate, phenylpropanoid, and ethylene) were detected using causal inference analysis. This analysis also revealed, for the first time, the activation of Z. mays resistance genes influencing the expression of specific A. flavus genes. Our results show that A. flavus seems to be reacting to a hostile environment resulting from the activation of resistance pathways in Z. mays. This study revealed the dynamic nature of the interaction between the two organisms.

Kilbournase, a protease-associated domain subtilase secreted by the fungal corn pathogen Stenocarpella maydis

Subtilases are a large family of serine proteases that occur throughout biology. A small subset contain protease-associated (PA) domains that are structurally separate from but encoded within the active site. In bacteria, subtilase PA domains function to recruit specific protein substrates. Here we demonstrate that a protease secreted by the fungal corn pathogen Stenocarpella maydis, which truncates corn ChitA chitinase, is a PA domain subtilase. Protease was purified from S. maydis cultures and tryptic peptides were analyzed by LC-MS/MS. Ions were mapped to two predicted PA domain subtilases. Yeast strains were engineered to express each protease. One failed to produce recombinant protein while the other secreted protease that truncated ChitA. This protease, that we named kilbournase, was purified and characterized. It cleaved multiple peptide bonds in the amino-terminal chitin binding domain of ChitA while leaving the catalytic domain intact. Kilbournase was more active on the ChitA-B73 alloform compared to ChitA-LH82 and did not cleave AtChitIV3, a homolog from Arabidopsis thaliana, indicating a high level of specificity. Truncation of corn ChitA by kilbournase resembles truncation of human C5a by Streptococcus pyogenes ScpA, arguing that PA domain proteases in bacteria and fungi may commonly target specific host proteins.

Dual function of a secreted fungalysin metalloprotease in Ustilago maydis

Fungalysins from several phytopathogenic fungi have been shown to be involved in cleavage of plant chitinases. While fungal chitinases are responsible for cell wall remodeling during growth and morphogenesis, plant chitinases are important components of immunity. This study describes a dual function of the Ustilago maydis fungalysin UmFly1 in modulation of both plant and fungal chitinases. Genetic, biochemical and microscopic experiments were performed to elucidate the in vitro and in planta functions of U. maydis UmFly1. U. maydis ∆umfly1 mutants show significantly reduced virulence, which coincides with reduced cleavage of the maize chitinase ZmChiA within its chitin-binding domain. Moreover, deletion of umfly1 affected the cell separation of haploid U. maydis sporidia. This phenotype is associated with posttranslational activation of the endogenous chitinase UmCts1. Genetic complementation of the ∆umfly1 mutant with a homologous gene from closely related, but nonpathogenic, yeast fully rescued the cell separation defect in vitro, but it could not recover the ∆umfly1 defect in virulence and cleavage of the maize chitinase. We report on the dual function of the secreted fungalysin UmFly1. We hypothesize that co-evolution of U. maydis with its host plant extended the endogenous function of UmFly1 towards the modulation of plant chitinase activity to promote infection.

Primary Structure Analysis of Antifungal Peptides from Cultivated and Wild Cereals

Cereal-derived bioactive peptides with antimicrobial activity have been poorly explored compared to those from dicotyledonous plants. Furthermore, there are a few reports addressing the structural differences between antimicrobial peptides (AMPs) from cultivated and wild cereals, which may shed light on significant varieties in the range and level of their antimicrobial activity. We performed a primary structure analysis of some antimicrobial peptides from wild and cultivated cereals to find out the features that are associated with the much higher antimicrobial resistance characteristic of wild plants. In this review, we identified and analyzed the main parameters determining significant antifungal activity. They relate to a high variability level in the sequences of C-terminal fragments and a high content of hydrophobic amino acid residues in the biologically active defensins in wild cereals, in contrast to AMPs from cultivated forms that usually exhibit weak, if any, activity. We analyzed the similarity of various physicochemical parameters between thionins and defensins. The presence of a high divergence on a fixed part of any polypeptide that is close to defensins could be a determining factor. For all of the currently known hevein-like peptides of cereals, we can say that the determining factor in this regard is the structure of the chitin-binding domain, and in particular, amino acid residues that are not directly involved in intermolecular interaction with chitin. The analysis of amino acid sequences of alpha-hairpinins (hairpin-like peptides) demonstrated much higher antifungal activity and more specificity of the peptides from wild cereals compared with those from wheat and corn, which may be associated with the presence of a mini cluster of positively charged amino acid residues. In addition, at least one hydrophobic residue may be responsible for binding to the components of fungal cell membranes.

Characterization of maize chitinase-A, a tough allergenic molecule

Food allergies are recognized as an increasing health concern. Proteins commonly identified as food allergens tend to have one of about 30 different biochemical activities. This leads to the assumption that food allergens must have specific structural features which causes their allergenicity. But these structural features are not completely understood. Uncovering the structural basis of allergenicity would allow improved diagnosis and therapy of allergies and would provide insights for safer food production. The availability of recombinant food allergens can accelerate their structural analysis and benefit specific studies in allergology. Plant chitinases are an example of food allergenic proteins for which structural analysis of allergenicity has only partially been reported. The recombinant maize chitinase, rChiA, was purified from Pichia pastoris extracellular medium by differential precipitation and cation exchange chromatography. Enzyme activity was evaluated by halo-assays and microcalorimetric procedures. rChiA modeling was performed by a two-step procedure, using the Swiss-Model server and Modeller software. Allergenicity of rChiA was verified by immunoblot assays with sera from allergic subjects. rChiA is active in the hydrolysis of glycol chitin and tetra-N-acetylchitotetraose and maintains its activity at high temperatures (70°C) and low pH (pH 3). The molecule is also reactive with IgE from sera of maize-allergic subjects. rChiA is a valuable molecule for further studies on structure-allergenicity relationships and as a tool for diagnosing allergies.

Recognition of corn defense chitinases by fungal polyglycine hydrolases

Polyglycine hydrolases (PGH)s are secreted fungal endoproteases that cleave peptide bonds in the polyglycine interdomain linker of ChitA chitinase, an antifungal protein from domesticated corn (Zea mays ssp. mays). These target-specific endoproteases are unusual because they do not cut a specific peptide bond but select one of many Gly-Gly bonds within the polyglycine region. Some Gly-Gly bonds are cleaved frequently while others are never cleaved. Moreover, we have previously shown that PGHs from different fungal pathogens prefer to cleave different Gly-Gly peptide bonds. It is not understood how PGHs selectively cleave the ChitA linker, especially because its polyglycine structure lacks peptide sidechains. To gain insights into this process we synthesized several peptide analogs of ChitA to evaluate them as potential substrates and inhibitors of Es-cmp, a PGH from the plant pathogenic fungus Epicoccum sorghi. Our results showed that part of the PGH recognition site for substrate chitinases is adjacent to the polyglycine linker on the carboxy side. More specifically, four amino acid residues were implicated, each spaced four residues apart on an alpha helix. Moreover, analogous peptides with selective Gly->sarcosine (N-methylglycine) mutations or a specific Ser->Thr mutation retained inhibitor activity but were no longer cleaved by PGH. Additonally, our findings suggest that peptide analogs of ChitA that inhibit PGH activity could be used to strengthen plant defenses.

Cloning of the Aegiceras corniculatum class I chitinase gene (AcCHI I) and the response of AcCHI I mRNA expression to cadmium stress

Chitinases in terrestrial plants have been reported these are involved in heavy metal tolerance/detoxification. This is the first attempt to reveal chitinase gene (AcCHI I) and its function on metal detoxification in mangroves Aegiceras corniculatum. RT-PCR and RACE techniques were used to clone AcCHI I, while real-time quantitative PCR was employed to assess AcCHI I mRNA expressions in response to Cadmium (Cd). The deduced AcCHI I protein consists of 316 amino acids, including a signal peptide region, a chitin-binding domain (CBD) and a catalytic domain. Protein homology modeling was performed to identify potential features in AcCHI I. The CBD structure of AcCHI I might be critical for metal tolerance/homeostasis of the plant. Clear tissue-specific differences in AcCHI I expression were detected, with higher transcript levels detected in leaves. Results demonstrated that a short duration of Cd exposure (e.g., 3 days) promoted AcCHI I expression in roots. Upregulated expression was also detected in leaves under 10 mg/kg Cd concentration stress. The present study demonstrates that AcCHI I may play an important role in Cd tolerance/homeostasis in the plant. Further studies of the AcCHI I protein, gene overexpression, the promoter and upstream regulation will be necessary for clarifying the functions of AcCHI I.

Synergistic Action of a Metalloprotease and a Serine Protease from Fusarium oxysporum f. sp. lycopersici Cleaves Chitin-Binding Tomato Chitinases, Reduces Their Antifungal Activity, and Enhances Fungal Virulence

As part of their defense strategy against fungal pathogens, plants secrete chitinases that degrade chitin, the major structural component of fungal cell walls. Some fungi are not sensitive to plant chitinases because they secrete chitin-binding effector proteins that protect their cell wall against these enzymes. However, it is not known how fungal pathogens that lack chitin-binding effectors overcome this plant defense barrier. Here, we investigated the ability of fungal tomato pathogens to cleave chitin-binding domain (CBD)-containing chitinases and its effect on fungal virulence. Four tomato CBD chitinases were produced in Pichia pastoris and were incubated with secreted proteins isolated from seven fungal tomato pathogens. Of these, Fusarium oxysporum f. sp. lycopersici, Verticillium dahliae, and Botrytis cinerea were able to cleave the extracellular tomato chitinases SlChi1 and SlChi13. Cleavage by F. oxysporum removed the CBD from the N-terminus, shown by mass spectrometry, and significantly reduced the chitinase and antifungal activity of both chitinases. Both secreted metalloprotease FoMep1 and serine protease FoSep1 were responsible for this cleavage. Double deletion mutants of FoMep1 and FoSep1 of F. oxysporum lacked chitinase cleavage activity on SlChi1 and SlChi13 and showed reduced virulence on tomato. These results demonstrate the importance of plant chitinase cleavage in fungal virulence.

Polyglycine hydrolases: Fungal β-lactamase-like endoproteases that cleave polyglycine regions within plant class IV chitinases

Polyglycine hydrolases are secreted fungal proteases that cleave glycine-glycine peptide bonds in the inter-domain linker region of specific plant defense chitinases. Previously, we reported the catalytic activity of polyglycine hydrolases from the phytopathogens Epicoccum sorghi (Es-cmp) and Cochliobolus carbonum (Bz-cmp). Here we report the identity of their encoding genes and the primary amino acid sequences of the proteins responsible for these activities. Peptides from a tryptic digest of Es-cmp were analyzed by LC-MS/MS and the spectra obtained were matched to a draft genome sequence of E. sorghi. From this analysis, a 642 amino acid protein containing a predicted β-lactamase catalytic region of 280 amino acids was identified. Heterologous strains of the yeast Pichia pastoris were created to express this protein and its homolog from C. carbonum from their cDNAs. Both strains produced recombinant proteins with polyglycine hydrolase activity as shown by SDS-PAGE and MALDI-MS based assays. Site directed mutagenesis was used to mutate the predicted catalytic serine of Es-cmp to glycine, resulting in loss of catalytic activity. BLAST searching of publicly available fungal genomes identified full-length homologous proteins in 11 other fungi of the class Dothideomycetes, and in three fungi of the related class Sordariomycetes while significant BLAST hits extended into the phylum Basidiomycota. Multiple sequence alignment led to the identification of a network of seven conserved tryptophans that surround the β-lactamase-like region. This is the first report of a predicted β-lactamase that is an endoprotease.

The battle in the apoplast: further insights into the roles of proteases and their inhibitors in plant-pathogen interactions

Upon host penetration, fungal pathogens secrete a plethora of effectors to promote disease, including proteases that degrade plant antimicrobial proteins, and protease inhibitors (PIs) that inhibit plant proteases with antimicrobial activity. Conversely, plants secrete proteases and PIs to protect themselves against pathogens or to mediate recognition of pathogen proteases and PIs, which leads to induction of defense responses. Many examples of proteases and PIs mediating effector-triggered immunity in host plants have been reported in the literature, but little is known about their role in compromising basal defense responses induced by microbe-associated molecular patterns. Recently, several reports appeared in literature on secreted fungal proteases that modify or degrade pathogenesis-related proteins, including plant chitinases or PIs that compromise their activities. This prompted us to review the recent advances on proteases and PIs involved in fungal virulence and plant defense. Proteases and PIs from plants and their fungal pathogens play an important role in the arms race between plants and pathogens, which has resulted in co-evolutionary diversification and adaptation shaping pathogen lifestyles.

Polyglycine hydrolases secreted by Pleosporineae fungi that target the linker region of plant class IV chitinases

Cmps (chitinase-modifying proteins) are fungal proteases that truncate plant class IV chitinases by cleaving near their N-termini. We previously described Fv-cmp, a fungalysin protease that cleaves a conserved glycine-cysteine bond within the hevein domain. In the present paper we describe a new type of cmp, polyglycine hydrolases, as proteases that selectively cleave glycine-glycine peptide bonds within the polyglycine linker of plant class IV chitinases. Polyglycine hydrolases were purified from Cochliobolus carbonum (syn. Bipolaris zeicola; Bz-cmp) and Epicoccum sorghi (syn. Phoma sorghina; Es-cmp) and were shown to cleave three different maize class IV chitinase substrates. The proteolytic cleavage sites were assessed by SDS/PAGE and MALDI-TOF-MS and indicated the cleavage of multiple peptide bonds within the polyglycine linker regions. Site-directed mutagenesis was used to produce mutants of maize ChitB chitinase in which two serine residues in its linker were systematically modified to glycine. Serine to glycine changes in the ChitB linker resulted in higher susceptibility to truncation by Bz-cmp and altered substrate specificity for Bz-cmp and Es-cmp, such that different glycine-glycine peptide bonds were cleaved. Removal of the hevein domain led to loss of Es-cmp activity, indicating that interactions outside of the active site are important for recognition. Our findings demonstrate that plant class IV chitinases with polyglycine linkers are targeted for truncation by selective polyglycine hydrolases that are secreted by plant pathogenic fungi. This novel proteolysis of polyglycine motifs is previously unreported, but the specificity is similar to that of bacterial lysostaphin proteases, which cleave pentaglycine cross-links from peptidoglycan.

Crystallographic structure of ChitA, a glycoside hydrolase family 19, plant class IV chitinase from Zea mays

Maize ChitA chitinase is composed of a small, hevein-like domain attached to a carboxy-terminal chitinase domain. During fungal ear rot, the hevein-like domain is cleaved by secreted fungal proteases to produce truncated forms of ChitA. Here, we report a structural and biochemical characterization of truncated ChitA (ChitA ΔN), which lacks the hevein-like domain. ChitA ΔN and a mutant form (ChitA ΔN-EQ) were expressed and purified; enzyme assays showed that ChitA ΔN activity was comparable to the full-length enzyme. Mutation of Glu62 to Gln (ChitA ΔN-EQ) abolished chitinase activity without disrupting substrate binding, demonstrating that Glu62 is directly involved in catalysis. A crystal structure of ChitA ΔN-EQ provided strong support for key roles for Glu62, Arg177, and Glu165 in hydrolysis, and for Ser103 and Tyr106 in substrate binding. These findings demonstrate that the hevein-like domain is not needed for enzyme activity. Moreover, comparison of the crystal structure of this plant class IV chitinase with structures from larger class I and II enzymes suggest that class IV chitinases have evolved to accommodate shorter substrates.

Truncation of class IV chitinases from Arabidopsis by secreted fungal proteases

Plant class IV chitinases have a small amino-terminal chitin-binding domain and a larger chitinase domain, and are involved in plant defence against fungal infection. Our previous work on the chitinases ChitA and ChitB from the model monocotyledon Zea mays showed that the chitin-binding domain is removed by secreted fungal proteases called fungalysins. In this article, we extend this work to dicotyledons. The effects of fungalysin-like proteases on four class IV chitinases from the model dicotyledon Arabidopsis thaliana were analysed. Four Arabidopsis chitinases were heterologously expressed in Pichia pastoris, purified and shown to have chitinase activity against a chitohexaose (dp6) substrate. The incubation of these four chitinases with Fv-cmp, a fungalysin protease secreted by Fusarium verticillioides, resulted in the truncation of AtchitIV3 and AtchitIV5. Moreover, incubation with secreted proteins from Alternaria brassicae, a pathogen of A. thaliana and brassica crops, also led to a similar truncation of AtchitIV3 and AtchitIV4. Our finding that class IV chitinases from both dicotyledons (A. thaliana) and monocotyledons (Z. mays) are truncated by proteases secreted by specialized pathogens of each plant suggests that this may be a general mechanism of plant-fungal pathogenicity.

Identification of a chitinase-modifying protein from Fusarium verticillioides: truncation of a host resistance protein by a fungalysin metalloprotease

Chitinase-modifying proteins (cmps) are proteases secreted by fungal pathogens that truncate the plant class IV chitinases ChitA and ChitB during maize ear rot. cmp activity has been characterized for Bipolaris zeicola and Stenocarpella maydis, but the identities of the proteases are not known. Here, we report that cmps are secreted by multiple species from the genus Fusarium, that cmp from Fusarium verticillioides (Fv-cmp) is a fungalysin metalloprotease, and that it cleaves within a sequence that is conserved in class IV chitinases. Protein extracts from Fusarium cultures were found to truncate ChitA and ChitB in vitro. Based on this activity, Fv-cmp was purified from F. verticillioides. N-terminal sequencing of truncated ChitA and MALDI-TOF-MS analysis of reaction products showed that Fv-cmp is an endoprotease that cleaves a peptide bond on the C-terminal side of the lectin domain. The N-terminal sequence of purified Fv-cmp was determined and compared with a set of predicted proteins, resulting in its identification as a zinc metalloprotease of the fungalysin family. Recombinant Fv-cmp also truncated ChitA, confirming its identity, but had reduced activity, suggesting that the recombinant protease did not mature efficiently from its propeptide-containing precursor. This is the first report of a fungalysin that targets a nonstructural host protein and the first to implicate this class of virulence-related proteases in plant disease.

A high-throughput matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry-based assay of chitinase activity

A high-throughput matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) assay is described for determination of chitolytic enzyme activity. The assay uses unmodified chitin oligosaccharide substrates and is readily achievable on a microliter scale (2μl of total volume containing 2μg of substrate and 1ng of protein). The speed and sensitivity of the assay make it potentially well suited for the high-throughput screening of chitinase inhibitors. The mass spectrum is acquired in approximately 2min, as opposed to typically 30-40min for a single run with a high-performance liquid chromatography (HPLC)-based assay. By using the multiple-place MALDI MS targets, we estimate that 100 assays could be run in approximately 2-3h without needing to remove the target from the instrument. In addition, because the substrate and product chitomers are visualized simultaneously in the TOF spectrum, this gives immediate information about the cleavage site and mechanism of the enzyme under study. The assay was used to monitor the purification and transgenic expression of plant class IV chitinases. By performing the assay with chitomer substrates and C-glycoside chitomer analogs, the enzyme mechanism of the class IV chitinases is described for the first time.