Perkins S J, Smith K F, Williams S C, Haris P I, Chapman D, Sim R B
Department of Biochemistry, Royal Free Hospital School of Medicine, London, U.K.
J Mol Biol. 1994 Apr 22;238(1):104-19. doi: 10.1006/jmbi.1994.1271.
The type A domain of the von Willebrand Factor is found also in the complement proteins factor B (FB), C2, CR3 and CR4, the integrins, collagen types VI, VII, XII and XIV, and other proteins. FB is a component of the alternative pathway of the complement system of immune defence, and is cleaved into the fragments Bb and Ba during complement activation. Bb contains a von Willebrand Factor type A (vWF) domain of unknown secondary structure and a serine proteinase (SP) domain, whereas Ba contains three short consensus repeat/complement control protein (SCR/CCP) domains. Fourier transform infrared (FT-IR) spectroscopy on a recombinant vWF domain and on FB and its Bb and Ba fragments shows a broad amide I band. In H2O buffer, second derivative spectra of the amide I band show subcomponents at 1654 to 1657 cm-1, which is typical of alpha-helix, and at 1676 to 1685 cm-1 and 1636 to 1637 cm-1, which are typical of beta-strand. alpha-Helix was detected in the vWF domain, the Bb fragment and FB, and the proportion of alpha-helix present decreased in that order. This shows that the vWF domain contains appreciable amounts of alpha-helix, while the SP and SCR/CCP domains are almost entirely beta-sheet in their secondary structures. Quantitative integration of the vWF FT-IR spectrum showed that this contained 31% alpha-helix and 36% beta-sheet. In 2H2O buffer, the alpha-helix content in the vWF domain is sensitive to the solvent, while the beta-sheet content is less so. An alignment of 75 vWF type A sequences from 25 proteins was used for averaged secondary structure predictions of the total length of 206 residues by the Robson and Chou-Fasman methods. In support of the FT-IR analysis, a total of at least five well-predicted alpha-helices (35% of residues) and at least five well-predicted beta-strands (21% of residues) were identified by both predictive methods, all of which were interspersed by regions of coil or turn conformations. Eight of the ten predicted alpha-helices and beta-strands form an alternating arrangement with each other. Since the predicted alpha-helices are mostly amphipathic, and since the alpha-helix FT-IR band is sensitive to solvent, the alpha-helices are inferred to be on the protein surface.(ABSTRACT TRUNCATED AT 400 WORDS)
血管性血友病因子的 A 型结构域也存在于补体蛋白 B 因子（FB）、C2、CR3 和 CR4、整合素、VI 型、VII 型、XII 型和 XIV 型胶原蛋白以及其他蛋白质中。FB 是免疫防御补体系统替代途径的一个组成部分，在补体激活过程中被切割成片段 Bb 和 Ba。Bb 包含一个二级结构未知的血管性血友病因子 A 型（vWF）结构域和一个丝氨酸蛋白酶（SP）结构域，而 Ba 包含三个短共有重复序列/补体控制蛋白（SCR/CCP）结构域。对重组 vWF 结构域以及 FB 及其 Bb 和 Ba 片段进行傅里叶变换红外（FT-IR）光谱分析，显示出一个宽泛的酰胺 I 带。在 H2O 缓冲液中，酰胺 I 带的二阶导数光谱显示在 1654 至 1657 cm-1 处有亚组分，这是α-螺旋的典型特征，在 1676 至 1685 cm-1 和 1636 至 1637 cm-1 处也有亚组分，这是β-链的典型特征。在 vWF 结构域、Bb 片段和 FB 中检测到了α-螺旋，且α-螺旋的存在比例按此顺序降低。这表明 vWF 结构域含有相当数量的α-螺旋，而 SP 和 SCR/CCP 结构域在二级结构上几乎完全是β-折叠。vWF 的 FT-IR 光谱定量积分显示其含有 31%的α-螺旋和 36%的β-折叠。在 2H2O 缓冲液中，vWF 结构域中的α-螺旋含量对溶剂敏感，而β-折叠含量则不太敏感。通过 Robson 方法和 Chou-Fasman 方法，利用来自 25 种蛋白质的 75 个 vWF A 型序列进行比对，对总共 206 个残基的全长进行平均二级结构预测。为支持 FT-IR 分析，两种预测方法均识别出总共至少五个预测良好的α-螺旋（占残基的 35%）和至少五个预测良好且β-链（占残基的 21%），所有这些都穿插着卷曲或转角构象区域。十个预测的α-螺旋和β-链中有八个相互交替排列。由于预测的α-螺旋大多具有两亲性，且α-螺旋的 FT-IR 带对溶剂敏感，因此推断α-螺旋位于蛋白质表面。（摘要截断于 400 字）
