Blanch E W, Hecht L, Barron L D
Chemistry Department, University of Glasgow, United Kingdom.
Protein Sci. 1999 Jun;8(6):1362-7. doi: 10.1110/ps.8.6.1362.
We have studied the conformation of beta-lactoglobulin in aqueous solution at room temperature over the pH range approximately 2.0-9.0 using vibrational Raman optical activity (ROA). The ROA spectra clearly show that the basic up and down beta-barrel core is preserved over the entire pH range, in agreement with other studies. However, from the shift of a sharp positive ROA band at approximately 1268 to approximately 1294 cm(-1) on going from pH values below that of the Tanford transition, which is centered at pH approximately 7.5, to values above, the Tanford transition appears to be associated with changes in the local conformations of residues in loop sequences possibly corresponding to a migration into the alpha-helical region of the Ramachandran surface from a nearby region. These changes may be related to those detected in X-ray crystal structures which revealed that the Tanford transition is associated with conformational changes in loops which form a doorway to the interior of the protein. The results illustrate how the ability of ROA to detect loop and turn structure separately from secondary structure is useful for studying conformational plasticity in proteins.
我们利用振动拉曼光学活性（ROA）研究了β-乳球蛋白在室温下、pH值约为2.0至9.0的水溶液中的构象。ROA光谱清楚地表明，在整个pH范围内，基本的上下β桶状核心得以保留，这与其他研究结果一致。然而，从pH值低于以约7.5为中心的坦福德转变值时，在约1268 cm⁻¹处的一个尖锐正ROA带向约1294 cm⁻¹处的移动，到pH值高于该转变值时，坦福德转变似乎与环序列中残基的局部构象变化有关，这可能对应于从附近区域迁移到拉马钱德兰表面的α螺旋区域。这些变化可能与在X射线晶体结构中检测到的变化有关，该结构表明坦福德转变与形成通往蛋白质内部通道的环中的构象变化有关。结果说明了ROA从二级结构中单独检测环和转角结构的能力对于研究蛋白质构象可塑性是如何有用的。
