Alb J G, Gedvilaite A, Cartee R T, Skinner H B, Bankaitis V A
Department of Cell Biology, University of Alabama at Birmingham 35294-0005, USA.
Proc Natl Acad Sci U S A. 1995 Sep 12;92(19):8826-30. doi: 10.1073/pnas.92.19.8826.
The mammalian phosphatidylinositol/phosphatidylcholine transfer proteins (PI-TPs) catalyze exchange of phosphatidylinositol (PI) or phosphatidylcholine (PC) between membrane bilayers in vitro. We find that Ser-25, Thr-59, Pro-78, and Glu-248 make up a set of rat (r) PI-TP residues, substitution of which effected a dramatic reduction in the relative specific activity for PI transfer activity without significant effect on PC transfer activity. Thr-59 was of particular interest as it is a conserved residue in a highly conserved consensus protein kinase C phosphorylation motif in metazoan PI-TPs. Replacement of Thr-59 with Ser, Gln, Val, Ile, Asn, Asp, or Glu effectively abolished PI transfer capability but was essentially silent with respect to PC transfer activity. These findings identify rPI-TP residues that likely cooperate to form a PI head-group binding/recognition site or that lie adjacent to such a site. Finally, the selective sensitivity of the PI transfer activity of rPI-TP to alteration of Thr-59 suggests a mechanism for in vivo regulation of rPI-TP activity.
哺乳动物的磷脂酰肌醇/磷脂酰胆碱转移蛋白（PI-TPs）在体外催化磷脂酰肌醇（PI）或磷脂酰胆碱（PC）在膜双层之间的交换。我们发现，Ser-25、Thr-59、Pro-78和Glu-248构成一组大鼠（r）PI-TP残基，替换这些残基会使PI转移活性的相对比活性显著降低，而对PC转移活性无显著影响。Thr-59特别引人关注，因为它是后生动物PI-TPs中高度保守的共有蛋白激酶C磷酸化基序中的一个保守残基。用Ser、Gln、Val、Ile、Asn、Asp或Glu替换Thr-59可有效消除PI转移能力，但对PC转移活性基本无影响。这些发现确定了rPI-TP残基，它们可能协同形成一个PI头部基团结合/识别位点或位于该位点附近。最后，rPI-TP的PI转移活性对Thr-59改变的选择性敏感性提示了一种体内调节rPI-TP活性的机制。
