O-sialoglycoprotein endopeptidases cleave the polypeptide backbone of membrane glycoproteins that contain clusters of O-linked sialoglycans. Osgep (O-sialoglycoprotein endopeptidase), also known as GCPL1, is a 335 amino acid protein that is a member of the peptidase M22 family. Osgep specifically cleaves the 31-Arg-l-Asp-32 bond in glycophorin A, but it does not cleave desialylated glycoproteins, unglycosylated proteins or glycoproteins that are only N-glycosylated. Though ubiquitously expressed at low levels, highest levels of Osgep are found in liver, skeletal muscle and kidney. OSGEPL1, also known as Qri7, is a 414 amino acid protein that belongs to the KAE1/YgjD family and exists as three alternatively spliced isoforms. In tRNAs that have codons beginning with adenine, OSGEPL1 is required for the formation of a threonylcarbamoyl group on adenosine.