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. 2019 Nov 5;294(50):19081–19098. doi: 10.1074/jbc.RA119.011153

Figure 1.

Figure 1.

Sec14-like PITPs and diversification of PtdIns(4)P signaling. A illustrates the concept that the biological outcome of PtdIns(4)P signaling in yeast is primarily determined by the Sec14-like PITP that stimulates activity of a PtdIns 4-OH kinase to produce a functionally channeled PtdIns(4)P pool. This strategy is a major mechanism for diversifying PtdIns(4)P signaling. B depicts a heterotypic PtdIns/“second lipid” exchange cycle where the second lipid (lipid X) is a priming lipid that potentiates presentation of PtdIns to the lipid kinase, thereby rendering the PtdIns a superior substrate for the kinase resulting in stimulation of PtdIns(4)P production (3, 4, 6). At left is shown the concept for the Sec14 PtdIns/PtdCho-exchange cycle where PtdIns(4)P is channeled to promotion of membrane trafficking from the TGN/endosomal system. At right is shown the general case proposed for Sec14-like PITPs that fail to bind PtdCho and for whom identification of the exchangeable lipid X is sought.