Penetration of lipid chains into transmembrane surfaces of membrane proteins: Studies with MscL
Penetration of lipid chains into transmembrane surfaces of membrane proteins: Studies with MscL
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DOI：
10.1529/biophysj.106.102210
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发表时间：
2007-05-10
影响因子：
3.4
通讯作者：
Lee, Anthony G.
中科院分区：
文献类型：
--
作者：
Carney, Joanne;East, J. Malcolm;Lee, Anthony G.
多螺旋膜蛋白的跨膜表面将是粗糙的，在跨膜α-螺旋之间有大小不一的空洞。通过膜中蛋白质周围的脂类分子有效地使表面溶剂化，需要脂类脂肪酰链能够进入空洞。这种可能性已经用荧光猝灭方法进行了研究。色氨酸残基被引入到大电导MSCL机械敏感通道的第一个跨膜α螺旋(M1)的面向脂质的位置；M1的N端的面向脂质的残基埋在蛋白质的跨膜表面之下。M1中面向脂质的Trp残基的荧光发射最大值与第二跨膜α螺旋(M2)中的Trp残基的荧光发射峰值相似，尽管M2中的面向脂质的残基位于蛋白质的表面。M1和M2膜周质侧色氨酸残基的荧光发射光谱符合介电常数呈谷状变化的模型，但膜的位置与细胞质侧面的最大荧光发射之间的关系更为复杂。M1中Trp残基的荧光被含溴脂肪酰链的磷脂有效地猝灭，表明脂链必须能够进入MSCL表面含Trp的空腔，从而导致表面的有效溶剂化。
The transmembrane surface of a multi-helix membrane protein will be rough with cavities of various sizes between the transmembrane alpha-helices. Efficient solvation of the surface by the lipid molecules that surround the protein in a membrane requires that the lipid fatty acyl chains be able to enter the cavities. This possibility has been investigated using fluorescence quenching methods. Trp residues have been introduced into lipid-facing sites in the first transmembrane alpha-helix ( M1) of the mechanosensitive channel of large- conductance MscL; lipid- facing residues at the N- terminal end of M1 are buried below the transmembrane surface of the protein. Fluorescence emission maxima for lipid- facing Trp residues in M1 vary with position in the bilayer comparably to those for Trp residues in the second transmembrane alpha-helix ( M2) despite the fact that lipid- facing residues in M2 are on the surface of the protein. Fluorescence emission spectra for most Trp residues on the periplasmic sides of M1 and M2 fit well to a model proposing a trough-like variation of dielectric constant across the membrane, but the relationship between location and fluorescence emission maximum on the cytoplasmic side of the membrane is more complex. The fluorescence of Trp residues in M1 is quenched efficiently by phospholipids with bromine-containing fatty acyl chains, showing that the lipid chains must be able to enter the Trp-containing cavities on the surface of MscL, resulting in efficient solvation of the surface.