RIAM/APBB1IP Antibody

APBB1IP (Amyloid beta A4 precursor protein-binding family B member 1 interacting protein; also PREL-1, Pro-rich protein 73, RARP1 and RIAM) is a member of the MRL family of proteins. Although its predicted MW is 73 kDa, it runs anomalously at 100-110 kDa in SDS-PAGE. It is expressed in megakaryocytes, T cells and fibroblasts. APBB1IP acts as a coordinator for Rap1 GTPase signaling. Rap1 both antagonizes Ras signaling, and is associated with beta 1 and beta 2 integrin-induced cell adhesion and cytoskeleton rearrangement. Within this context, APBB1IP operates as a cytosolic adaptor protein that induces integrin activation by recruiting talin and RAP1 to the cell membrane, and by mediating Profilin and VASP protein polymerizatiuon of actin. Human APBB1IP is 666 amino acids (aa) in length. It contains a poly-Pro sequence (aa 129-148), a Ras-association domain (aa 176-263), a PH domain (aa 310-419), and a large poly-Pro region (aa 503-640). There are multiple potential isoform variants. One contains a deletion of aa 152-177 coupled to a 27 aa substitution for aa 262-666, a second possesses a 21 aa substitution for aa 152‑666, and a third shows a deletion of aa 386-390 coupled to a five aa substitution for aa 417-666. Over aa 2-89, human APBB1IP shares 97% aa sequence identity with mouse APBB1IP.