Williams K A, Farrow N A, Deber C M, Kay L E
Division of Biochemistry Research, Hospital for Sick Children, Toronto, Ontario, Canada.
Biochemistry. 1996 Apr 23;35(16):5145-57. doi: 10.1021/bi952897w.
The structure and dynamics of the 53-residue filamentous bacteriophage IKe major coat protein in fully protonated myristoyllysophosphatidylglycerol (MPG) micelles were characterized using multinuclear solution NMR spectroscopy. Detergent-solubilized coat protein [sequence: see text] mimics the membrane-bound "assembly intermediate" form of the coat protein which occurs during part of the phage life cycle. NMR studies of the IKe coat protein show that the coat protein is largely alpha-helical, exhibiting a long amphipathic surface. helix (Asn 4 to Ser 26) and a shorter "micelle-spanning" C-terminal helix which begins at TRP 29 and continues at least to Phe 48. Pro 30 likely occurs in the first turn of the C-terminal helix, where it is ideally situated given the hydrogen bonding and steric restrictions imposed by this residue. The similarity of 15N relaxation values (T1, T2, and NOE and 500 MHz and T2 at 600 MHz) among much of the N-terminal helix and all of the TM helix indicates that the N-terminal helix is as closely associated with the micelle as the TM helix. The description of the protein in the micelle is supported by the observation of NOEs between lysolipid protons and protein amide protons between asn 8 and Ser 50. The N-terminal and TM helices exhibit substantial mobility on the microsecond to second time scale, which likely reflects changes in the orientation between the two helices. The overall findings serve to clarify the role of individual residues in the context of a TM alpha-helix and provide an understanding of the secondary structure, dynamics, and aqueous and micellar environments of the coat protein.
利用多核溶液核磁共振光谱对53个残基的丝状噬菌体IKe主要外壳蛋白在完全质子化的肉豆蔻酰赖氨酰磷脂酰甘油（MPG）胶束中的结构和动力学进行了表征。去污剂增溶的外壳蛋白[序列：见正文]模拟了在噬菌体生命周期的一部分期间出现的外壳蛋白的膜结合“组装中间体”形式。对IKe外壳蛋白的核磁共振研究表明，该外壳蛋白主要是α螺旋结构，具有一个长的两亲性表面螺旋（Asn 4至Ser 26）和一个较短的“跨胶束”C端螺旋，该螺旋从TRP 29开始，至少持续到Phe 48。Pro 30可能出现在C端螺旋的第一圈，鉴于该残基施加的氢键和空间限制，它处于理想位置。N端螺旋的大部分和所有跨膜螺旋之间的15N弛豫值（T1、T2和NOE，500 MHz时）以及600 MHz时的T2相似，这表明N端螺旋与跨膜螺旋一样紧密地与胶束结合。在溶血脂质质子和Asn 8至Ser 50之间的蛋白质酰胺质子之间观察到的NOE支持了胶束中蛋白质的描述。N端和跨膜螺旋在微秒到秒的时间尺度上表现出显著的流动性，这可能反映了两个螺旋之间取向的变化。总体研究结果有助于阐明单个残基在跨膜α螺旋背景下的作用，并提供对外壳蛋白二级结构、动力学以及水性和胶束环境的理解。
