In order to inhibit the activity of plant extracellular enzymes, β(1,3) and β(1,6)endoglucanases (EGases), involved in plant defense responses, including during the infection process, glucanase inhibitor proteins (GIPs) are secreted by species of the genus Phytophthora. Besides the structural homology to the chymotrypsin class of serine proteases (SP), GIPs, due to the absence of an intact catalytic triad, lack proteolytic activity. For that reason, they belong to a broader class of nonfunctional proteins caled serine protease homologs (SPH). Despite the high homology of GIPs to the SP subfamily S1A, some questions remain regarding the expression patterns and potential roles of different GIPs during pathogenesis and also their possible interaction with host EGases in the plant apoplast.
