title: Recognition of corn defense chitinases by fungal polyglycine hydrolases.
abstract: 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.
authors.affiliation: Mycotoxin Prevention and Applied Microbiology Research Unit, National Center for Agriculture Utilization Research, Peoria, IL, 61604.
authors.forename: Todd A
authors.initials: TA
authors.lastname: Naumann
authors.affiliation: Renewable Product Technology Research Unit, National Center for Agriculture Utilization Research, Peoria, IL, 61604.
authors.forename: Erica L
authors.initials: EL
authors.lastname: Bakota
authors.affiliation: Functional Foods Research Unit, National Center for Agriculture Utilization Research, Peoria, IL, 61604.
authors.forename: Neil P J
authors.initials: NPJ
authors.lastname: Price
mesh_terms: D001203:Ascomycota / Q000201:enzymology*; D002688:Chitinases / Q000737:chemistry* / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry* / Q000378:metabolism; D010447:Peptide Hydrolases / Q000737:chemistry* / Q000378:metabolism; D010935:Plant Diseases / Q000382:microbiology; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism; D003313:Zea mays / Q000201:enzymology* / Q000382:microbiology
chemical_list: D005656:Fungal Proteins; D010940:Plant Proteins; D002688:Chitinases; D010447:Peptide Hydrolases
keywords: SXXK motif; beta-lactamase; effectors; family S12; host-pathogen interactions; penicillin-binding protein; penicillin-recognizing protein; peptides; plant defense; protease; proteinase