Eilers M, Shekar S C, Shieh T, Smith S O, Fleming P J
Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, NY 11794-5215, USA.
Proc Natl Acad Sci U S A. 2000 May 23;97(11):5796-801. doi: 10.1073/pnas.97.11.5796.
Helix packing is important in the folding, stability, and association of membrane proteins. Packing analysis of the helical portions of 7 integral membrane proteins and 37 soluble proteins show that the helices in membrane proteins have higher packing values (0.431) than in soluble proteins (0.405). The highest packing values in integral membrane proteins originate from small hydrophobic (G and A) and small hydroxyl-containing (S and T) amino acids, whereas in soluble proteins large hydrophobic and aromatic residues have the highest packing values. The highest packing values for membrane proteins are found in the transmembrane helix-helix interfaces. Glycine and alanine have the highest occurrence among the buried amino acids in membrane proteins, whereas leucine and alanine are the most common buried residue in soluble proteins. These observations are consistent with a shorter axial separation between helices in membrane proteins. The tight helix packing revealed in this analysis contributes to membrane protein stability and likely compensates for the lack of the hydrophobic effect as a driving force for helix-helix association in membranes.
螺旋堆积对于膜蛋白的折叠、稳定性及缔合十分重要。对7种整合膜蛋白和37种可溶性蛋白的螺旋部分进行堆积分析表明，膜蛋白中的螺旋具有比可溶性蛋白更高的堆积值（0.431对0.405）。整合膜蛋白中最高的堆积值源自小的疏水性（甘氨酸和丙氨酸）和含羟基的小氨基酸（丝氨酸和苏氨酸），而在可溶性蛋白中，大的疏水性和芳香族残基具有最高的堆积值。膜蛋白的最高堆积值出现在跨膜螺旋-螺旋界面处。甘氨酸和丙氨酸在膜蛋白中埋藏氨基酸中出现频率最高，而亮氨酸和丙氨酸是可溶性蛋白中最常见的埋藏残基。这些观察结果与膜蛋白中螺旋间较短的轴向间距一致。该分析中揭示的紧密螺旋堆积有助于膜蛋白的稳定性，并且可能弥补了作为膜中螺旋-螺旋缔合驱动力的疏水作用的不足。
