Ahn T, Kim H
Department of Biological Sciences, Korea Advanced Institute of Science and Technology, 373-1 Kusong-Dong, Yusong-Gu, Taejon, 305-701, Korea.
J Biol Chem. 1998 Aug 21;273(34):21692-8. doi: 10.1074/jbc.273.34.21692.
The effect of nonlamellar-prone lipids, diacylglycerol (DG) and phosphatidylethanolamine (PE), on the ATPase activity of SecA was examined. When Escherichia coli PE of the standard vesicles composed of 60 mol% of this lipid and 40 mol% of dioleoylphosphatidylglycerol (DOPG) is gradually replaced with either dioleoylglycerol (DOG) or dioeloyl PE (DOPE), the ATPase activity of SecA present together increased appreciably. On the other hand, when E. coli PE of the standard vesicles was replaced with DOG analogs, the SecA ATPase activity decreased slightly, and when replaced with phosphatidylcholine the decrease in the ATPase activity was more appreciable. When DOPE or E. coli PE was added to PC vesicles, the SecA ATPase activity was enhanced only slightly, suggesting that the hexagonal II structure per se is not important for the ATPase activity increase. It was observed that DOG induced phase separation of PG, and the lamellar-hexagonal II (L-HII) transition temperature of vesicles decreased by about 10 degreesC. The DOG analogs had no effect on these properties, suggesting the importance of the phase separation of PG and the decrease of L-HII transition temperature of lipid bilayers to the SecA ATPase activity. The phase separation of PG by Ca2+ also brought about increased ATPase activity of SecA, underlining the importance of phase separation of PG for the enzyme activity. The incorporation of DOG or DOPE in the vesicle also increased the amount of SecA bound to model membranes and the extent of SecA penetration into the membrane. Studies with vesicles without SecA showed increased exposure of hydrophobic acyl chains when the DOG was present. Taken together, these observations suggest that the phase separation of PG and/or the bilayer penetration of SecA are mainly responsible for the enhanced SecA-vesicle interaction with concomitant increase in SecA ATPase activity.
研究了不易形成非片层结构的脂质二酰甘油（DG）和磷脂酰乙醇胺（PE）对SecA的ATP酶活性的影响。当由60摩尔%的该脂质和40摩尔%的二油酰磷脂酰甘油（DOPG）组成的标准囊泡中的大肠杆菌PE逐渐被二油酰甘油（DOG）或二油酰PE（DOPE）取代时，同时存在的SecA的ATP酶活性明显增加。另一方面，当标准囊泡中的大肠杆菌PE被DOG类似物取代时，SecA的ATP酶活性略有下降，而当被磷脂酰胆碱取代时，ATP酶活性的下降更为明显。当将DOPE或大肠杆菌PE添加到PC囊泡中时，SecA的ATP酶活性仅略有增强，这表明六方II结构本身对于ATP酶活性的增加并不重要。观察到DOG诱导了PG的相分离，并且囊泡的片层-六方II（L-HII）转变温度降低了约10℃。DOG类似物对这些性质没有影响，这表明PG的相分离和脂质双层的L-HII转变温度降低对SecA的ATP酶活性很重要。Ca2+引起的PG相分离也导致SecA的ATP酶活性增加，强调了PG相分离对酶活性的重要性。在囊泡中掺入DOG或DOPE也增加了与模型膜结合的SecA的量以及SecA渗透到膜中的程度。对没有SecA的囊泡的研究表明，当存在DOG时，疏水酰链的暴露增加。综上所述，这些观察结果表明，PG的相分离和/或SecA的双层渗透主要负责增强的SecA-囊泡相互作用以及SecA的ATP酶活性随之增加。
