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. Author manuscript; available in PMC: 2011 Oct 1.
Published in final edited form as: Clin Lipidol. 2010 Dec 1;5(6):867–897. doi: 10.2217/clp.10.67

Figure 1. Transfer versus nanoreactor models for phosphatidylinositol transfer protein function.

Figure 1

(A) Lipid transfer models invoke a vectorial carrier function for PITPs where PtdIns is transported from membranes of high PtdIns concentration (endoplasmic reticulum) to relatively PtdIns-poor membranes of the distal compartments of the secretory pathway which house PtdIns-4-OH kinase activity (TGN/endosomes or plasma membrane). These models describe productive transfer as involving one heterotypic exchange reaction per donor and acceptor membrane (i.e., two such exchanges per cycle). (B) The ‘nanoreactor’ model predicts that PITPs stimulate PI4-OH kinase activity by executing multiple rounds of phospholipid-exchange at a single membrane site. Only heterotypic exchange reactions generate PtdIns configurations suitable for effective PtdIns presentation.

PI4P: Phosphatidylinositol-4-phosphate; PITP: Phosphatidylinositol transfer protein; PO4: Phosphate; PtdCho: Phosphatidylcholine; PtdIns: Phosphatidylinositol.

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