Secretion-associated Ras-related GTPase 1B (SAR1B)

Secretion-associated Ras-related GTPase 1B (SAR1B) is a small GTPase enzyme critical for the formation and function of COPII-coated vesicles, which mediate the transport of newly synthesized proteins and lipids from the endoplasmic reticulum to the Golgi apparatus[1][2][3][4]. SAR1B alternates between active (GTP-bound) and inactive (GDP-bound) states, enabling membrane curvature, vesicle budding, and cargo selection, including the transport of lipid-carrying lipoproteins such as chylomicrons and apolipoproteins APOB and APOA1[1][2][4]. SAR1B is highly expressed in enterocytes, where it is essential for intestinal lipid absorption and the secretion of fat-soluble vitamins; mutations in SAR1B cause chylomicron retention disease (Anderson’s disease), leading to severe fat and vitamin malabsorption[3][4][5]. SAR1B also indirectly regulates TORC1 signaling and cellular metabolism, and plays a role in the cellular ER stress response by modulating protein homeostasis processes[1][2]. SAR1B belongs to the Ras-related small GTPase family and is functionally distinct but partially redundant with its paralog SAR1A[5].

Other names

Small COPII coat GTPase SAR1BSARA2SARBGTBPBGTP-binding protein BGTP-binding protein SAR1bGTP-binding protein SaraANDDCMRD2310075M17RikSAR1 homolog BSAR1a gene homolog 2

Not applicable (no approved direct SAR1B-modulating drugs). Experimental: Gene replacement or upregulation of SAR1A can functionally compensate for SAR1B deficiency[5].