Kim J, Kim H
Department of Biological Science and Engineering, Korea Advanced Institute of Science, Seoul.
Biochim Biophys Acta. 1989 Jul 24;983(1):1-8. doi: 10.1016/0005-2736(89)90372-6.
The alpha-lactalbumin segment which penetrates into phosphatidylserine/phosphatidylethanolamine vesicle bilayer under acidic condition was photoactively labeled with 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine [( 125I]TID) which had been partitioned into the hydrophobic interior of the bilayer. The hydrophobically labeled amino acid residues were identified by trypsin digestion of the alpha-lactalbumin/vesicle complex, extraction and Edman degradation of the membrane embedded fragment. The results are consistent with a notion that the segment exists in the membrane as an alpha-helix and that only one surface of this alpha-helix is exposed to the hydrophobic interior of the bilayer. Possible models are: (a) a loop of tightly held alpha-helix penetrating deep into the bilayer and (b) the helix being located on the interface between bilayer and the aqueous solution. The time-dependent [125I]TID labeling process revealed that the middle part of this segment goes into the bilayer first and is then followed by both ends. The penetration rate is comparable to that of the fusion of the lipid vesicles of the same composition by alpha-lactalbumin at the same pH, which further supports that the penetration is the cause of fusion.
在酸性条件下穿透磷脂酰丝氨酸/磷脂酰乙醇胺囊泡双层的α-乳白蛋白片段，用已分配到双层疏水内部的3-(三氟甲基)-3-(间-[¹²⁵I]碘苯基)重氮甲烷([¹²⁵I]TID)进行光活性标记。通过对α-乳白蛋白/囊泡复合物进行胰蛋白酶消化、提取并对嵌入膜的片段进行埃德曼降解，来鉴定疏水标记的氨基酸残基。结果与这样一种观点一致，即该片段在膜中以α-螺旋形式存在，且该α-螺旋只有一个表面暴露于双层的疏水内部。可能的模型有：(a) 一段紧密缠绕的α-螺旋深入双层内部的环；(b) 螺旋位于双层与水溶液的界面上。随时间变化的[¹²⁵I]TID标记过程表明，该片段的中部首先进入双层，随后是两端。穿透速率与相同pH下α-乳白蛋白对相同组成脂质囊泡的融合速率相当，这进一步支持了穿透是融合的原因这一观点。
