SAR1B Human

GTP-Binding Protein SAR1B, also known as Secretion Associated Ras Related GTPase 1B, is a small GTPase that plays a crucial role in the transport of proteins from the endoplasmic reticulum (ER) to the Golgi apparatus. This protein is part of the COPII coat complex, which is essential for vesicle-mediated transport within cells.

The SAR1B gene is located on chromosome 5 at the cytoband q31.1 and spans approximately 48,122 base pairs. It encodes a protein that consists of 198 amino acids with a molecular weight of around 22 kDa . The protein functions as a homodimer and is activated by the guanine nucleotide exchange factor PREB .

SAR1B cycles between an active GTP-bound state and an inactive GDP-bound state. In its active form, SAR1B inserts into the ER membrane, where it recruits other components of the COPII coat complex . This complex is responsible for the sorting of cargo proteins and the deformation and budding of membranes into vesicles destined for the Golgi apparatus .

The proper functioning of SAR1B is critical for maintaining cellular homeostasis and efficient protein trafficking. Defects in the SAR1B gene can lead to Chylomicron Retention Disease (CMRD), also known as Anderson Disease. This condition is characterized by the inability to properly secrete chylomicrons, leading to fat malabsorption and other related symptoms .

SAR1B is involved in several biological pathways, including the SARS-CoV-2 infection pathway and the trafficking of the cystic fibrosis transmembrane conductance regulator (CFTR) protein . It also synergizes with the cargo receptor SURF4 to mediate the export of lipoproteins from the ER, thereby regulating lipid homeostasis .