Anti-S-Arrestin (SAG, S-AG, 48kD Protein, Retinal S-antigen, Rod Photoreceptor Arrestin)

The arrestin proteins are a family of regulators of cell signaling of G protein-coupled receptors (GPCR). Visual arrestin was first discovered as a result of the experimental model of human uveitis, an autoimmune disease of the eye. In this model, called experimental allergic uveitis, animals were injected with extracts made from the retina of the same species mixed with Freund's complete adjuvant. The animals mounted a strong immune response to the extract, and the antibody response was used to identify several immunogenic retinal proteins. One of these was called S-antigen, for soluble antigen. The protein was found to be abundant in retina, about 48kD in molecular weight, and localized in the outer segments of the photoreceptors (1, 2). Several years later, Hermann Kühn and colleagues discovered that this protein binds to phosphorylated rhodopsin and prevents this protein from activating transducin (3, 4, 5). Transducin is a typical heterotrimeric G protein, composed of alpha and betagamma subunits. Rhodopsin phosphorylation is mediated by Rhodopsin kinase (a.k.a. GRK1), the prototypic member of a family of GPCR kinases. Since the S-antigen protein arrested the activity of rhodopsin it was renamed arrestin, and became the prototypic member of the arrestin protein family. Subsequently, Robert Lefkowitz and colleagues discovered a related protein which bound to phosphorylated beta-adrenergic GPCRs and prevented these proteins from activating their specific heterotrimeric G proteins (6). Because of this relationship to the beta-adrenergic receptor and functional and structural similarities to visual arrestin this protein was named beta-arrestin. The beta-adrenergic receptor was phosphorylated by the beta-adrenergic receptor kinase (a.k.a. GRK2), an enzyme belonging to GPCR kinase family. Studies of visual transduction therefore aided greatly in understanding other kinds of GPCR signaling. In mammals, there are four arrestin isoforms, Visual arrestin (a.k.a. S-antigen and arrestin-1) and cone arrestin (a.k.a. arrestin-4) are largely confined to photoreceptors. beta-arrestin 1 (a.k.a. arrestin 2) and beta-arrestin-2 (a.k.a. arrestin-3) are ubiquitous and regulate non-visual GPCRs. The HGNC name for this protein is SAG. Applications: Suitable for use in Immunofluorescence and Western Blot. Other applications not tested. Recommended Dilution: Immunofluorescence: ~1:1000, Western Blot: ~1:5000, A suitable control tissue is retinal homogenate. The arrestin protein runs at about ~48kD on SDS-PAGE gels., Optimal dilutions to be determined by the researcher. Storage and Stability: May be stored at 4°C for short-term only. Aliquot to avoid repeated freezing and thawing. Store at -20°C. Aliquots are stable for 12 months. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap.