title: Structure of the glucanase inhibitor protein (GIP) family from phytophthora species suggests coevolution with plant endo-beta-1,3-glucanases.
abstract: During invasion of their plant hosts, species of the oomycete genus Phytophthora secrete glucanase inhibitor proteins (GIPs) into the plant apoplast, which bind and inhibit the activity of plant extracellular endo-beta-1,3-glucanases (EGases). GIPs show structural homology to the chymotrypsin class of serine proteases (SP) but lack proteolytic activity due to the absence of an intact catalytic triad and, thus, belong to a broader class of proteins called serine protease homologs (SPH). To study the evolutionary relationship between GIPs and functional SP, database searches were used to identify 48 GIP homologs in the P. sojae, P. ramorum, and P. infestans genomes, composing GIPs, SPH, and potentially functional SP. Analyses of P. infestans-inoculated tomato leaves showed that P. infestans GIPs and tomato EGases are present in the apoplast and form stable complexes in planta. Studies of the temporal expression of a four-membered GIP family from P. infestans (PiGIP1 to PiGIP4) further revealed that the genes show distinctly different patterns during an infection timecourse. Codon evolution analyses of GIP homologs identified several positively selected peptide sites and structural modeling revealed them to be in close proximity to rapidly evolving EGase residues, suggesting that the interaction between GIPs and EGases has the hallmarks of a coevolving molecular arms race.
authors.affiliation: Department of Plant Biology, Cornell University, Ithaca, NY 14853, U.S.A.
authors.forename: Cynthia M B
authors.initials: CM
authors.lastname: Damasceno
authors.forename: John G
authors.initials: JG
authors.lastname: Bishop
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Ripoll
authors.forename: Joe
authors.initials: J
authors.lastname: Win
authors.forename: Sophien
authors.initials: S
authors.lastname: Kamoun
authors.forename: Jocelyn K C
authors.initials: JK
authors.lastname: Rose
mesh_terms: D020418:Algal Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D015153:Blotting, Western; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism*; D019143:Evolution, Molecular; D043326:Glucan 1,3-beta-Glucosidase / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D010838:Phytophthora / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
chemical_list: D020418:Algal Proteins; D004791:Enzyme Inhibitors; D010940:Plant Proteins; D043326:Glucan 1,3-beta-Glucosidase