Figure 4.

Models for cPLA₂α and AGPAT3/LPAAT3 activities contributing to COPI vesicle and Golgi membrane tubule formation. (A) Flat membrane that will be modified by curve producing proteins; (B) Arf1 and coatomer binding deforms membranes, initiating the first steps of vesiculation or tubulation; (B to C) AGPAT3/LPAAT3 activity produces unsaturated PA, a lipid that resists positive curvature; (B to D) cPLA₂α activity produces LPC, a positive curvature stabilizing and tubule inducing lipid; (C and D to E) LPC stabilizes positive curvature of the bud and unsaturated PA stabilizes negative curvature at the bud neck; (F) The concerted PA production activities of AGPAT3/LPAAT3 and PLD2 at the bud neck help to recruit BARS and aide vesicle fission; (G) PLA₂ activity can induce membrane curvature and tubulation in the absence of Arf1 and coatomer.