title: The polygalacturonase-inhibiting protein PGIP2 of Phaseolus vulgaris has evolved a mixed mode of inhibition of endopolygalacturonase PG1 of Botrytis cinerea.
abstract: Botrytis cinerea is a phytopathogenic fungus that causes gray mold in >1,000 plant species. During infection, it secretes several endopolygalacturonases (PGs) to degrade cell wall pectin, and among them, BcPG1 is constitutively expressed and is an important virulence factor. To counteract the action of PGs, plants express polygalacturonase-inhibiting proteins (PGIPs) that have been shown to inhibit a variety of PGs with different inhibition kinetics, both competitive and noncompetitive. The PG-PGIP interaction promotes the accumulation of oligogalacturonides, fragments of the plant cell wall that are general elicitors of plant defense responses. Here, we characterize the enzymatic activity of BcPG1 and investigate its interaction with PGIP isoform 2 from Phaseolus vulgaris (PvPGIP2) by means of inhibition assays, homology modeling, and molecular docking simulations. Our results indicate a mixed mode of inhibition. This is compatible with a model for the interaction where PvPGIP2 binds the N-terminal portion of BcPG1, partially covering its active site and decreasing the enzyme affinity for the substrate. The structural framework provided by the docking model is confirmed by site-directed mutagenesis of the residues that distinguish PvPGIP2 from the isoform PvPGIP1. The finding that PvPGIP2 inhibits BcPG1 with a mixed-type kinetics further indicates the versatility of PGIPs to evolve different recognition specificities.
authors.affiliation: Dipartimento di Biologia Vegetale, Università di Roma La Sapienza, 00185 Rome, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Sicilia
authors.forename: Juan
authors.initials: J
authors.lastname: Fernandez-Recio
authors.forename: Claudio
authors.initials: C
authors.lastname: Caprari
authors.forename: Giulia
authors.initials: G
authors.lastname: De Lorenzo
authors.forename: Demetrius
authors.initials: D
authors.lastname: Tsernoglou
authors.forename: Felice
authors.initials: F
authors.lastname: Cervone
authors.forename: Luca
authors.initials: L
authors.lastname: Federici
mesh_terms: D001665:Binding Sites; D020171:Botrytis / Q000201:enzymology* / Q000502:physiology; D007700:Kinetics; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D027805:Phaseolus / Q000378:metabolism* / Q000382:microbiology; D010940:Plant Proteins / Q000378:metabolism* / Q000494:pharmacology; D011096:Polygalacturonase / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D010940:Plant Proteins; D011096:Polygalacturonase