Aranda Roman, Levin Elena J, Schotte Friedrich, Anfinrud Philip A, Phillips George N
Department of Biomolecular Chemistry, University of Wisconsin, Madison, USA.
Acta Crystallogr D Biol Crystallogr. 2006 Jul;62(Pt 7):776-83. doi: 10.1107/S0907444906017318. Epub 2006 Jun 20.
Picosecond time-resolved crystallography was used to follow the dissociation of carbon monoxide from the heme pocket of a mutant sperm whale myoglobin and the resultant conformational changes. Electron-density maps have previously been created at various time points and used to describe amino-acid side-chain and carbon monoxide movements. In this work, difference refinement was employed to generate atomic coordinates at each time point in order to create a more explicit quantitative representation of the photo-dissociation process. After photolysis the carbon monoxide moves to a docking site, causing rearrangements in the heme-pocket residues, the coordinate changes of which can be plotted as a function of time. These include rotations of the heme-pocket phenylalanine concomitant with movement of the distal histidine toward the solvent, potentially allowing carbon monoxide movement in and out of the protein and proximal displacement of the heme iron. The degree of relaxation toward the intermediate and deoxy states was probed by analysis of the coordinate movements in the time-resolved models, revealing a non-linear progression toward the unbound state with coordinate movements that begin in the heme-pocket area and then propagate throughout the rest of the protein.
皮秒时间分辨晶体学被用于追踪一氧化碳从突变型抹香鲸肌红蛋白的血红素口袋中解离以及由此产生的构象变化。此前已在不同时间点创建电子密度图，并用于描述氨基酸侧链和一氧化碳的移动。在这项工作中，采用差分精修来生成每个时间点的原子坐标，以便对光解离过程创建更明确的定量表示。光解后，一氧化碳移动到一个对接位点，导致血红素口袋残基发生重排，其坐标变化可作为时间的函数绘制出来。这些变化包括血红素口袋苯丙氨酸的旋转，同时远端组氨酸向溶剂方向移动，这可能使一氧化碳能够进出蛋白质，并使血红素铁发生近端位移。通过分析时间分辨模型中的坐标移动，探究了向中间态和脱氧态弛豫的程度，结果显示向未结合态的进展是非线性的，坐标移动始于血红素口袋区域，然后传播到蛋白质的其余部分。
