Fig. 6

Model of alternating access mechanism in Vrg4. a Vrg4 adopts an inward open state with the binding site orientated towards the cytosol. GDP-mannose binds, resulting in the fast interconversion to the outward open state b, facing the Golgi lumen. c Following release of the GDP-mannose, GMP binds the transporter. The smaller size of GMP results in less efficient transport, resulting in a slower interconversion back to the inward open state d The key gating helices are TM1, 2 and 3, 4 that alternate around the central binding site. e Short chain lipids are necessary to facilitate the movement of the gating helices, with the transporter being inactive in longer chain lipids