Renin R (Renin Receptor; also ATPase H + -transporting lysosomal accessory/interacting protein 2, M8.9 and ELDF10) is a 39-45kD protein that belongs to no known family. It is expressed on the surface of macrophages, vascular smooth muscle cells, renal mesangial cells and T cells. Renin R has at least two functions. First, it binds both renin and prorenin, promoting the conversion of angiotensinogen to angiotensin I. Second, its ligation induces PAI-1 synthesis. Mature human Renin R is a type I transmembrane protein 334 amino acids (aa) in length. It contains a 286 aa extracellular region (aa 17-302) and a 27 aa cytoplasmic tail. It is believed to form homodimers. Potential isoforms exist. One termed M8.9 shows a deletion of aa 1-252 and constitutes a component of the vacuolar proton ATPase. Two others show an alternate start site at Met77, and a deletion of aa 101-132. Over aa 17-302, the human Renin R shares 95% aa identity with the mouse Renin R.