Sperm leucyl aminopeptidases (S-LAPs) are a closely related family of 8 proteins belonging to MEROPS family M17 that are specifically expressed in sperm. They have expanded and diverged from the ancestral grsm gene, but unlike that gene product, the S-LAPs lack critical catalytic residues at the active site and are not functional as aminopeptidases. However, S-LAPs must have acquired novel, as yet undetermined, functions in sperm because each member is required for male fertility. (Adapted from FBrf0213467 and FBrf0241579.)