Wakasugi K, Ishimori K, Imai K, Wada Y, Morishima I
Division of Molecular Engineering, Graduate School of Engineering, Kyoto University, Japan.
J Biol Chem. 1994 Jul 22;269(29):18750-6.
In the genes of alpha- and beta-subunits of hemoglobin, Go showed that modules F1, F2 + F3, and F4 correspond to exons 1, 2, and 3, respectively (Go, M. (1981) Nature 291, 90). The analysis of the correlation of function with its exon pattern showed that the residues associated with the defined function are concentrated in the specific exons encoding the "module" (Eaton, W.A. (1980) Nature 284, 183). To investigate the functional and structural significance of the "modular structure," we engineered a "chimera" subunit, in which module F4 of the beta-subunit was replaced by that of the alpha-subunit by use of mutagenesis. The NMR and resonance Raman spectra of the isolated "chimera beta alpha-subunit" have revealed that it has a beta-subunit-like heme environmental structure. However, the gel chromatography and NMR spectra of mixtures of the chimera and native subunits clearly showed that the chimera beta alpha-subunit binds specifically to the beta-subunit to form a heterotetramer, not to the alpha-subunit. These results led us to conclude that the predominant role of the module F4 is the subunit association and suggest that the modules are structural and functional units that have advantages in producing stable functional proteins.
在血红蛋白α亚基和β亚基的基因中，Go发现模块F1、F2 + F3和F4分别对应于外显子1、2和3（Go，M.（1981年）《自然》291，90）。对功能与其外显子模式相关性的分析表明，与特定功能相关的残基集中在编码“模块”的特定外显子中（伊顿，W.A.（1980年）《自然》284，183）。为了研究“模块化结构”的功能和结构意义，我们构建了一个“嵌合”亚基，其中通过诱变将β亚基的模块F4替换为α亚基的模块F4。分离出的“嵌合β-α亚基”的核磁共振（NMR）和共振拉曼光谱显示，它具有类似β亚基的血红素环境结构。然而，嵌合亚基与天然亚基混合物的凝胶色谱和核磁共振光谱清楚地表明，嵌合β-α亚基特异性地与β亚基结合形成异源四聚体，而不与α亚基结合。这些结果使我们得出结论，模块F4的主要作用是亚基缔合，并表明这些模块是结构和功能单元，在产生稳定的功能蛋白方面具有优势。
