Peptidase M48C Ste24p loiP-like, integral membrane protein
This subfamily contains peptidase M48 Ste24p protease loiP (formerly yggG)-like family are mostly uncharacterized proteins that include E. coli loiP and ycaLG, considered to be putative metallopeptidases, containing a zinc-binding motif, HEXXH, and a COOH-terminal ER retrieval signal (KKXX). They proteolytically remove the C-terminal three residues of farnesylated proteins. They are integral membrane proteins associated with the endoplasmic reticulum and golgi, binding one zinc ion per subunit. In eukaryotes, Ste24p is required for the first NH2-terminal proteolytic processing event within the a-factor precursor, which takes place after COOH-terminal CAAX modification (C is cysteine; A is usually aliphatic; X is one of several amino acids) is complete. Mutation studies have shown that the HEXXH protease motif, which is extracellular but adjacent to a transmembrane domain and therefore close to the membrane surface, is critical for Ste24p activity. LoiP has been shown to be a metallopeptidase that cleaves its targets preferentially between Phe-Phe residues. It is upregulated when bacteria are subjected to media of low osmolarity, thus yggG was named LoiP (low osmolarity induced protease). Proper membrane localization of LoiP may depend on YfgC, another putative metalloprotease in this subfamily.
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