Inaba K, Ishimori K, Morishima I
Graduate School of Engineering, Kyoto University, Kyoto, 606-850, Japan.
J Mol Biol. 1998;283(1):311-27. doi: 10.1006/jmbi.1998.2073.
To investigate structural and functional significance of a newly proposed structural unit in globins, the "heme binding module", we synthesized a "heme binding module"-substituted chimeric globin and characterized its function and structure. In our previous study we proposed that the heme binding module, corresponding to the segment from Leu(F1) to Phe(G5) in hemoglobin alpha-subunit, plays a key role in constructing the heme proximal structure in globins. The replacement of the heme binding module in myoglobin with that of hemoglobin alpha-subunit converted the absorption spectra into that of the alpha-subunit, and, in the resonance Raman spectra, the vibration mode characteristic of myoglobin completely disappeared after the module replacement. The hyperfine-shifted NMR resonances for the cyanide-bound form of the module-substituted myoglobin also revealed that the orientation of the axial histidine is close to that of the alpha-subunit rather than that of myoglobin, while the deviations of the resonance positions of the NMR signals from the amino acid residues located in the distal site were subtle, supporting the preferential structural alterations in the heme proximal site. The present finding for the structural alterations in the module-substituted myoglobin confirms that the heme binding module can be a segment regulating the heme proximal structure in globin proteins.
为了研究球蛋白中一个新提出的结构单元“血红素结合模块”的结构和功能意义，我们合成了一种“血红素结合模块”取代的嵌合球蛋白，并对其功能和结构进行了表征。在我们之前的研究中，我们提出血红素结合模块对应于血红蛋白α亚基中从Leu(F1)到Phe(G5)的片段，在构建球蛋白的血红素近端结构中起关键作用。用血红蛋白α亚基的血红素结合模块替换肌红蛋白中的该模块后，吸收光谱转变为α亚基的吸收光谱，并且在共振拉曼光谱中，模块替换后肌红蛋白特有的振动模式完全消失。模块取代的肌红蛋白与氰化物结合形式的超精细位移核磁共振共振也表明，轴向组氨酸的取向更接近α亚基而非肌红蛋白，而位于远端位点的氨基酸残基的核磁共振信号共振位置的偏差很细微，这支持了血红素近端位点的优先结构改变。目前关于模块取代的肌红蛋白结构改变的发现证实，血红素结合模块可以是调节球蛋白中血红素近端结构的一个片段。
