Lambright D G, Balasubramanian S, Decatur S M, Boxer S G
Department of Chemistry, Stanford University, California 94305-5080.
Biochemistry. 1994 May 10;33(18):5518-25. doi: 10.1021/bi00184a021.
In order for diatomic ligands to enter and exit myoglobin, there must be substantial displacements of amino acid side chains from their positions in the static X-ray structure. One pathway, involving Arg/Lys45, His64, and Val68, has been studied in greatest detail. In an earlier study (Lambright et al., 1989) we reported the surprising result that mutation of the surface residue Lys45 to arginine lowers the inner barrier to CO rebinding. Until then, it had been thought that this barrier primarily involves interior distal pocket residues such as His64 and Val68. In this report, we present a detailed study of the CO rebinding kinetics in aqueous solution of a series of single- and double-site mutants of human myoglobin at positions 64, 68, 45, and 60. On the basis of the observed kinetics, we propose that the effect of surface residue 45 on the inner barrier can be explained by a chain of interactions between surface and pocket residues. Very large, and in some cases unexpected, changes are observed in the kinetics of recombination and in the partitioning between geminate and bimolecular recombination.
为了使双原子配体进出肌红蛋白，氨基酸侧链必须相对于其在静态X射线结构中的位置发生显著位移。其中一条涉及精氨酸/赖氨酸45、组氨酸64和缬氨酸68的途径得到了最详细的研究。在早期的一项研究中（兰布赖特等人，1989年），我们报告了一个惊人的结果，即表面残基赖氨酸45突变为精氨酸会降低一氧化碳重新结合的内部屏障。在此之前，人们一直认为这个屏障主要涉及内部远端口袋残基，如组氨酸64和缬氨酸68。在本报告中，我们对人肌红蛋白在64、68、45和60位的一系列单位点和双位点突变体在水溶液中的一氧化碳重新结合动力学进行了详细研究。根据观察到的动力学，我们提出表面残基45对内部屏障的影响可以通过表面和口袋残基之间的一系列相互作用来解释。在重组动力学以及双分子重组和双分子重组之间的分配中观察到了非常大的，在某些情况下是意想不到的变化。
