Collectrin (also Transmembrane protein 27) is a 37-43kD member of the MEM27 family of proteins. It is expressed on pancreatic beta-cells where it regulates insulin secretion, and on renal tubular epithelium where it mediates amino acid transport. Mature mouse Collectrin is a 208aa type I transmembrane glycoptotein. It contains a 127aa extracellular region (aa15-141) and a 60aa cytoplasmic domain (aa163-222). Collectrin dimerizes on the cell surface, and undergoes proteolytic cleavage to generate a 26kD soluble fragment. Over aa15-144, mouse Collectrin shares 92% and 86% aa identity with rat and human Collectrin, respectively.