Endopeptidases belonging to membrane-bound hydrogen evolving hydrogenase group. In hydrogenase 3 from E coli, the maturation of the large subunit (HycE) requires the cleavage of a C-terminal peptide by the endopeptidase HycI, before the final formation of the [NiFe] metallocenter. HycI protease is a monomer and lacks characteristic signature motifs of serine, zinc, cysteine, or acid proteases and thus its cleavage reaction is not inhibited by conventional inhibitors of serine and metalloproteases. Such hydrogenases as those from Methanosarcina barkeri (EchCE) and Rhodospirillum rubrum (CooLH) also belong to this group of membrane-bound hydrogen evolving hydrogenase. Sequence comparison of the large subunits from related hydrogenase indicates that in contrast to EchE (358 amino acids) and CooH (361 amino acids), the large subunit HycE (569 amino acids) contains an extra carboxy-terminal stretch of 32 amino acids that is cleaved during the maturation process. In the absence of this C-terminal stretch, there is no homolog of endopeptidase HycI found in these two related hydrogenase.
Jiyao W et al.(2023). "The conserved domain database in 2023.",