SQAPI, aspartic acid inhibitor first isolated from squash, inhibits a wide range of aspartic proteinases. This particular family of PAAPIs (proteinaceous aspartic acid inhibitors) seems to have evolved quite recently from an ancestral cystatin. Struc ...
SQAPI, aspartic acid inhibitor first isolated from squash, inhibits a wide range of aspartic proteinases. This particular family of PAAPIs (proteinaceous aspartic acid inhibitors) seems to have evolved quite recently from an ancestral cystatin. Structurally it consists of a four-stranded anti-parallel beta-sheet gripping an alpha-helix in much the same manner that a hand grips a tennis racket. The unstructured N-terminus and the loop connecting beta-strands 1 and 2 are important for pepsin inhibition, but the loop connecting strands 3 and 4 is not [1].