Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, New South Wales 2109, Australia.
Biochemistry. 2010 Jun 29;49(25):5278-89. doi: 10.1021/bi100111c.
A striking feature of the CLIC (chloride intracellular channel) protein family is the ability of its members to convert between a soluble state and an integral membrane channel form. Direct evidence of the structural transition required for the CLIC protein to autonomously insert into the membrane is lacking, largely because of the challenge of probing the conformation of the membrane-bound protein. However, insights into the CLIC transmembrane form can be gained by biophysical methods such as fluorescence resonance energy transfer (FRET) spectroscopy. This approach was used to measure distances from tryptophan 35, located within the CLIC1 putative N-domain transmembrane region, to three native cysteine residues within the C-terminal domain. These distances were computed both in aqueous solution and upon the addition of membrane vesicles. The FRET distances were used as constraints for modeling of a structure for the CLIC1 integral membrane form. The data are suggestive of a large conformational unfolding occurring between the N- and C-domains of CLIC1 upon interaction with the membrane. Consistent with previous findings, the N-terminal domain of CLIC1 is likely to insert into the lipid bilayer, while the C-domain remains in solution on the extravesicular side of the membrane.
CLIC（氯离子细胞内通道）蛋白家族的一个显著特点是其成员能够在可溶性状态和完整膜通道形式之间转换。CLIC 蛋白自主插入膜中所需的结构转变的直接证据是缺乏的，这主要是因为探测膜结合蛋白构象的挑战。然而，通过荧光共振能量转移（FRET）光谱等生物物理方法可以深入了解 CLIC 的跨膜形式。该方法用于测量位于 CLIC1 假定的 N 结构域跨膜区域内的色氨酸 35 与 C 末端结构域内三个天然半胱氨酸残基之间的距离。这些距离在水溶液中和添加膜囊泡后都进行了计算。FRET 距离被用作建模 CLIC1 完整膜形式结构的约束条件。这些数据表明，在与膜相互作用时，CLIC1 的 N 和 C 结构域之间发生了大的构象展开。与先前的发现一致，CLIC1 的 N 端结构域可能插入脂质双层，而 C 结构域在膜的囊泡外侧面上仍留在溶液中。
