Primary structure of brevilysin L4, an enzymatically active fragment of a disintegrin precursor from Gloydius halys brevicaudus venom

Brevilysin L4 (L4) is a non-hemorrhagic P-I class metalloprotease (MP) isolated from Gloydius halys brevicaudus venom. Its complete amino acid sequence has been determined. L4 is a single-chain polypeptide and highly homologous to those of other snake venom MPs. A zinc-binding motif, HExxHxxGxxH, is located at residues 142-152. A characteristic feature of L4 is the presence of a spacer sequence (LRTDTVS) at the C-terminal that links metalloprotease and disintegrin domains and is usually removed by post-translational proteolysis, suggesting that L4 is expressed together with a spacer region and a disintegrin domain at the C-terminal. The nucleotide sequence of a cDNA clone encoding L4 has revealed that L4 is a disintegrin precursor and produced as a P-II class MP. The disintegrin coded after L4 sequence was brevicaudin 1, a disintegrin previously isolated from the same venom. P-II class MPs have been suspected to undergo autoproteolysis to release disintegrins. Although being P-I class MP, L4 itself autocatalytically degrades with a half-life of 30 min at pH 8.5 and 37 °C in the absence of Ca2+. Sequence analysis of several fragment peptides produced during the autolysis of L4 indicated that more than 40 peptide bonds were split, and the cleavages of Ser60-Asn61, Thr99-Ala100, and Phe103-Asp104 bonds may trigger the autoproteolysis. Addition of Ca2+ completely suppressed the cleavage of these particular bonds, resulting in a marked prevention of autoproteolysis. Thus, L4 provides a good model for the investigation of autolysis of some MPs.