ULTRAFAST MEASUREMENTS OF GEMINATE RECOMBINATION OF NO WITH SITE-SPECIFIC MUTANTS OF HUMAN MYOGLOBIN

作     者：PETRICH, JW LAMBRY, JC BALASUBRAMANIAN, S LAMBRIGHT, DG BOXER, SG MARTIN, JL 

作者机构：STANFORD UNIV DEPT CHEM STANFORD CA 94305 USA ECOLE POLYTECH ENSTA INSERM U275 OPT APPL LAB F-91128 PALAISEAU FRANCE 

出 版 物：《JOURNAL OF MOLECULAR BIOLOGY》 (分子生物学杂志)

年 卷 期：1994年第238卷第3期

页      面：437-444页

核心收录：

学科分类：0710[理学-生物学] 071010[理学-生物化学与分子生物学] 07[理学] 

主　　题：HUMAN MYOGLOBIN MUTAGENESIS KINETICS STRUCTURE-FUNCTION RELATIONSHIPS PICOSECOND TIMESCALE 

摘      要：Flash photolysis studies of NO recombination to heme proteins offer a direct probe of protein structural changes on the tens of picoseconds timescale where they can be compared with molecular dynamics simulations. The geminate recombination of NO to site-specific mutants of human myoglobin (Mb) was studied following photodissociation of the MbNO form. Single amino acid changes were introduced at positions Val68, His64, Lys45 and Asp60 because motions of residues at these positions are generally regarded as important for the mechanism of ligand binding. In sharp contrast to the properties of simple porphyrin-NO complexes, the rebinding kinetics are found to be non-exponential for all mutants, even in aqueous solution at 298 K. The Val68 and His64 mutants substantially affect the NO rebinding rates but, surprisingly, so do changes on the protein surface that are further away from the iron. These changes in kinetics occur on a tens of picoseconds timescale, and therefore there is either a fast communication between protein residues over quite long distances or there are subtle differences in protein structure that exert great control over the reaction dynamics. Various models for the rebinding kinetics are evaluated. A model-free approach to data analysis using the maximum entropy method is found to be most useful. This analysis shows that the rate distributions are very different for the mutants, but are generally bimodal.