LRMP is a 74-76kD protein that is associated with the ER. In contrast to its name, LRMP expression is not restricted to lymphoid cell types. Cells known to express LRMP include stomach chief cells, seminal vesicle cuboidal epithelium, neurons, germinal center B cells, cortical thymocytes, and cells of the taste buds. LRMP is suggested to participate in intracellular peptide transport. It is also reported to physically interact with IP3RP. Human LRMP is a 56kD, single-pass transmembrane (TM) protein that is 499aa in length. It contains a 439aa cytoplasmic region aa1-439, a 21aa TM segment aa440-460 and a 39aa luminal domain aa461-499 that is cleaved after Ala469 to generate a type IV TM protein. LRMP runs anomalously in SDS-Page, and the 75kD form may be linked to an isoform that utilizes a Leu start site 56aa upstream of the start site for the 499aa isoform. In this regard, a human isoform has been reported that is 62kD in size. Mature mouse LRMP is 509aa in length (after cleavage) and runs at 65kD in SDS-PAGE. Over aa143-292, human LRMP shares 93% aa identity with mouse LRMP.