This short highly conserved region, containing the GCGEQ motif, is found in protease inhibitors and complement factors, members of A2MF family. These proteins utilise a unique trapping mechanism that pseudo-inhibits proteases regardless of their catalytic class [ PUBMED:4201304 PUBMED:26100869 … expand

This short highly conserved region, containing the GCGEQ motif, is found in protease inhibitors and complement factors, members of A2MF family. These proteins utilise a unique trapping mechanism that pseudo-inhibits proteases regardless of their catalytic class [ PUBMED:4201304 PUBMED:26100869 ]. With a few exceptions (e.g., complement C5), A2MF proteins contain an internal thioester formed between the cysteine and a glutamine side chain in the conserved GCGEQ motif. After bait region cleavage, this thioester is exposed and can react with nucleophilic amine and hydroxyl groups on proteins and carbohydrates. As a result, the nascent activated A2MF protein may become covalently linked to the bait region-cleaving protease. The trapped protease remains catalytically active but is prevented from cleaving protein substrates through steric hindrance imposed by the inhibitor following a proteolytically triggered conformational change.