Postnikova G B
Biokhimiia. 1996 Jun;61(6):947-67.
The review briefly summarizes the results of spin-label studies of conformational transitions in monomeric globins (myoglobin, leghemoglobin, erythrocruorin) as well as in another heme-containing protein, cytochrome c, induced by heme ligands and pH. In contrast with integral methods of investigation, for proteins with a known spatial structure the use of the spin-labelling technique makes it possible to obtain information on the conformational behaviour of the isolated parts of the protein structure which, alongside with the results obtained by other physico-chemical methods, allows a conclusion on the nature of conformational movements in the protein during its functioning. The experimental results fit well into the model which represents a Mb-like structure as composed of three independent rigid helical fragments: AE(ABCDE), F and GH, whose reciprocal arrangement is controlled by N- and C-terminal salt bridges. Synchronous displacement of the above fragments relative to one another, which is due either to the ligand attachment and structural changes in the heme complex or to disturbances in ionic interactions at the N- and/or C-end(s) of the structure under effect of pH or allosteric effectors, might serve as a structural basis for homo- and heterotropic regulation in hemoglobin. Similarly, the spin label method allows for tracing and obtaining important information about local conformational events in cytochrome c which in the native protein are associated with a change in pH in the range of 5-13 and are accompanied by the substitution of the heme sixth ligand, Met-80, by Lys-79 (pH 9.3), and then by Tyr-67 (pK 11.1). Local changes in the conformation and dynamic properties of native cytochrome c provide, if necessary, global changes in its structure upon alkaline denaturation. It was found that substitution of the heme protein ligand, Met-80, by the external ligand, cyanide, markedly alters the dynamic properties of the polypeptide chain segment 67-75 adjacent to Met-80.
本综述简要总结了自旋标记研究的结果，该研究涉及血红素配体和pH值诱导的单体珠蛋白（肌红蛋白、豆血红蛋白、蚯蚓血红蛋白）以及另一种含血红素蛋白细胞色素c的构象转变。与整体研究方法不同，对于具有已知空间结构的蛋白质，使用自旋标记技术能够获取有关蛋白质结构孤立部分构象行为的信息，这些信息与其他物理化学方法所得结果一起，有助于推断蛋白质在其功能发挥过程中构象运动的性质。实验结果与一个模型非常吻合，该模型将肌红蛋白样结构描述为由三个独立的刚性螺旋片段组成：AE(ABCDE)、F和GH，它们的相互排列由N端和C端盐桥控制。上述片段彼此之间的同步位移，要么是由于配体附着和血红素复合物中的结构变化，要么是由于在pH值或变构效应剂作用下结构的N端和/或C端离子相互作用受到干扰，这可能是血红蛋白同源和异源调节的结构基础。同样，自旋标记方法能够追踪并获取有关细胞色素c局部构象事件的重要信息，在天然蛋白质中，这些事件与pH值在5 - 13范围内的变化相关，并伴随着血红素第六配体Met - 80被Lys - 79（pH 9.3）取代，随后被Tyr - 67（pK 11.1）取代。天然细胞色素c构象和动态特性的局部变化在必要时会导致其在碱性变性时结构发生整体变化。研究发现，用外部配体氰化物取代血红素蛋白配体Met - 80会显著改变与Met - 80相邻的多肽链片段67 - 75的动态特性。
