The saccharopepsin inhibitor is highly specific for the aspartic peptidase saccharopepsin. It is largely unstructured in the absence of saccharopepsin [1], but in the presence, the inhibitor undergoes a conformation change forming an almost perfect alpha-helix from Asn2 to Met32 in the active site cleft of the peptidase.

1: IA3, an aspartic proteinase inhibitor from Saccharomyces cerevisiae, is intrinsically unstructured in solution. Green TB, Ganesh O, Perry K, Smith L, Phylip LH, Logan TM, Hagen SJ, Dunn BM, Edison AS; Biochemistry. 2004;43:4071-4081. PMID:15065849