SAC1-like domains of yeast SAC1, INP52, and INP53 and of human synaptojanin encode polyphosphoinositide phosphatases

被引:315
作者
Guo, SL
Stolz, LE
Lemrow, SM
York, JD
机构
[1] Duke Univ, Med Ctr, Dept Pharmacol & Canc Biol, Durham, NC 27710 USA
[2] Duke Univ, Med Ctr, Dept Biochem, Durham, NC 27710 USA
关键词
D O I
10.1074/jbc.274.19.12990
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The SAC1 gene product has been implicated in the regulation of actin cytoskeleton, secretion from the Golgi, and microsomal ATP transport; yet its function is unknown. Within SAC1 is an evolutionarily conserved 300-amino acid region, designated a SAC1-like domain, that is also present at the amino termini of the inositol polyphosphate 5-phosphatases, mammalian synaptojanin, and certain yeast INP5 gene products. Here we report that SAC1-like domains have intrinsic enzymatic activity that defines a new class of polyphosphoinositide phosphatase (PPIPase), Purified recombinant SAC1-like domains convert yeast lipids phosphatidylinositol (PI) S-phosphate, PI 4-phosphate, and PI 3,5-bisphosphate to PI, whereas PI 4,5-bisphosphate is not a substrate. Yeast lacking Sac1p exhibit 10-, 2.5-, and a-fold increases in the cellular levels of PI 4-phosphate, PI 3,5-bisphosphate, and PI 3-phosphate, respectively. The 5-phosphatase domains of synaptojanin, Inp52p, and Inp53p are also catalytic, thus representing the first examples of an inositol signaling protein with two distinct lipid phosphatase active sites within a single polypeptide chain. Together, our data provide a long sought mechanism as to how defects in Sac1p overcome certain actin mutants and bypass the requirement for yeast phosphatidylinositol/phosphatidylcholine transfer protein, Sec14p. We demonstrate that PPIPase activity is a key regulator of membrane trafficking and actin cytoskeleton organization and suggest signaling roles for phosphoinositides other than PI 4,5-bisphosphate in these processes. Additionally, the tethering of PPIPase and B-phosphatase activities indicate a novel mechanism by which concerted phosphoinositide hydrolysis participates in membrane trafficking.
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页码:12990 / 12995
页数:6
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