The superfamily includes the imelysin peptidase, a M75 peptidase first identified in Pseudomonas aeruginosa and Algp7, a cell-surface alginate-binding protein, that was characterised in Sphingomonas sp. A1 and functions as a concentrator of the polysaccharide in the cell-surface pit. His201 and Glu204 are completely conserved in M75 and occur in an HXXE motif that is also found in family M14.

Based on the primary structure and genetic organisation in the bacterial genome, Algp7 was found to be homologous to an M75 peptidase motif-containing EfeO, a component of a ferrous ion transporter. Although a metal-binding motif, HxxE, conserved in zinc ion-dependent M75 peptidases is also found in Algp7, the crystal structure of Algp7 contains no metal even at the motif. The protein consists of two structurally similar up-and-down helical bundles as the basic scaffold. A deep cleft between the bundles is sufficiently large to accommodate macromolecules such as alginate polysaccharide PMID:21238429. DOI:.org/10.1016/j.bbrc.2011.01.043, PFAM:PF09375