Different effects of lipid chain length on the two sides of a membrane and the lipid annulus of MscL
Different effects of lipid chain length on the two sides of a membrane and the lipid annulus of MscL
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DOI：
10.1529/biophysj.107.105130
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发表时间：
2007-07-01
影响因子：
3.4
通讯作者：
Lee, Anthony G.
中科院分区：
文献类型：
--
作者：
Powl, Andrew M.;East, J. Malcolm;Lee, Anthony G.
淬火的。含溴脂肪酸酰基链的脂质对膜蛋白中色氨酸残基的荧光为测量脂质-蛋白结合常数提供了一种强有力的技术。将单个Trp残基放置在结核分枝杆菌大电导MscL的机械敏感通道的周质和细胞质两侧，分别测量MscL两个面上的脂质结合常数。脂质结合的链长依赖性在MscL的两侧是不同的，在细胞质侧的链长依赖性比在质周侧的链长依赖性更明显。为了确定脂质结合常数是否受到不与MscL直接接触的脂质分子（散装脂质）的性质的影响，系统中存在的散装脂质的数量发生了变化。发现短链磷脂二十二烷基磷脂酰胆碱的结合常数与脂质/MscL五聚体的摩尔比在500:1-50:1范围内无关，表明脂质结合常数在很大程度上取决于脂质分子与MscL直接相互作用的性质。这些结果指向一个模型，其中位于膜蛋白跨膜表面的脂质分子（环状脂质分子），通过在膜蛋白与周围脂质双分子层之间的相互作用中发挥主导作用，可以有效地缓冲膜蛋白免受大体积脂质双分子层性质变化的影响。
Quenching of the. uorescence of Trp residues in a membrane protein by lipids with bromine-containing fatty acyl chains provides a powerful technique for measuring lipid-protein binding constants. Single Trp residues have been placed on the periplasmic and cytoplasmic sides of the mechanosensitive channel of large conductance MscL from Mycobacterium tuberculosis to measure, separately, lipid binding constants on the two faces of MscL. The chain-length dependence of lipid binding was found to be different on the two sides of MscL, the chain-length dependence being more marked on the cytoplasmic than on the periplasmic side. To determine if lipid binding constants are affected by the properties of the lipid molecules not in direct contact with MscL (the bulk lipid), the amount of bulk lipid present in the system was varied. The binding constant of the short-chain phospholipid didodecylphosphatidylcholine was found to be independent of the molar ratio of lipid/MscL pentamer over the range 500: 1-50: 1, suggesting that lipid binding constants are determined largely by the properties of the lipid molecules interacting directly with MscL. These results point to a model in which lipid molecules located on the transmembrane surface of a membrane protein (the annular lipid molecules), by playing a dominant role in the interaction between a membrane protein and the surrounding lipid bilayer, could effectively buffer the membrane protein from changes in the properties of the bulk lipid bilayer.