SAR1A

SAR1A or Sar1 is a protein involved in membrane trafficking. It is a monomeric small GTPase found in COPII vesicles. It regulates the assembly and disassembly of COPII coats.

GDP-bound Sar1 interacts with the membrane-bound exchange factor Sec12 and exchanges its bound GDP for GTP. The hydrophobic N-terminus of Sar1-GTP then locates it to the membrane, where it serves as the binding site for the Sec23/Sec24 protein coat complex. After the vesicle coat is completely assembled and the vesicle is released from the donor membrane, the Sec23 subunit promotes Sar1 GTPase activity, which triggers the disassembly of the COPII coat.