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. Author manuscript; available in PMC: 2017 Mar 30.
Published in final edited form as: Subcell Biochem. 2012;59:271–287. doi: 10.1007/978-94-007-3015-1_9

Fig. 9.3.

Fig. 9.3

Heterotypic exchange promotes Ptdlns presentation. Heterotypic exchange reactions can support Ptdlns presentation by two different models. a PtdCho vectorial displaces a Sec14p bound Ptdlns in a head-first manner. The displaced Ptdlns exits the binding pocket through a portal distinct from the portal through which PtdCho invades. Ptdlns4-OH Kinase (not shown) modifies the exiting Ptdlns during this exchange. b A second mode by which heterotypic exchange promotes Ptdlns presentation is by frustration of an invading Ptdlns. In this mode, Ptdlns attempts to invade into the hydrophobic pocket of a PtdCho bound Sec14p. The bound PtdCho frustrates the Ptdlns, allowing Ptdlns 4-OH kinase to modify its substrate. Both models satisfy the requirement that Ptd-4-phosphate cannot collapse back into the hydrophobic pocket, as this complex results in locked Sec14p-PIP species that cannot be reversed by phospholipid exchange.