Zymogenic latency in an ∼ 250-million-year-old astacin metallopeptidase

The horseshoe crab Limulus polyphemus is one of few extant Limulus species, which date back to ∼ 250 million years ago under the conservation of a common Bauplan documented by fossil records. It possesses the only proteolytic blood-coagulation and innate immunity system outside vertebrates and is a model organism for the study of the evolution and function of peptidases. The astacins are a family of metallopeptidases that share a central ∼ 200-residue catalytic domain (CD), which is found in>1000 species across holozoans and, sporadically, bacteria. Here, the zymogen of an astacin from L. polyphemus was crystallized and its structure was solved. A 34-residue, mostly unstructured pro-peptide (PP) traverses, and thus blocks, the active-site cleft of the CD in the opposite direction to a substrate. A central `PP motif' (F35-E-G-D-I39) adopts a loop structure which positions Asp38 to bind the catalytic metal, replacing the solvent molecule required for catalysis in the mature enzyme according to an `aspartate-switch' mechanism. Maturation cleavage of the PP liberates the cleft and causes the rearrangement of an `activation segment'. Moreover, the mature N-terminus is repositioned to penetrate the CD moiety and is anchored to a buried `family-specific' glutamate. Overall, this mechanism of latency is reminiscent of that of the other three astacins with known zymogenic and mature structures, namely crayfish astacin, human meprin β and bacterial myroilysin, but each shows speci...

Source: Acta Crystallographica Section D - October 20, 2022 Category: Biochemistry Authors: Guevara, T. Rodr í guez-Banqueri, A. St ö cker, W. Becker-Pauly, C. Gomis-R ü th, F.X. Tags: metallopeptidase zymogenic latency astacin metallopeptidase Limulus polyphemus horseshoe crab aspartate-switch mechanism catalytic domain pro-peptide research papers Source Type: research