Ikura T, Go N, Kohda D, Inagaki F, Yanagawa H, Kawabata M, Kawabata S, Iwanaga S, Noguti T, Go M
Department of Chemistry, Faculty of Science, Kyoto University, Japan.
Proteins. 1993 Aug;16(4):341-56. doi: 10.1002/prot.340160404.
Proteins consist of structural units such as globular domains, secondary structures, and modules. Modules were originally defined by partitioning a globular domain into compact regions, each of which is a contiguous polypeptide segment having a compact conformation. Since modules show close correlations with the intron positions of genes, they are regarded as primordial polypeptide pieces encoded by exons and shuffled, leading to yield new combination of them in early biological evolution. Do modules maintain their native conformations in solution when they are excised at their boundaries? In order to find answers to this question, we have synthesized modules of barnase, one of the bacterial RNases, and studied the solution structures of modules M2 (amino acid residues 24-52) and M3 (52-73) by 2D NMR studies. Some local secondary structures, alpha-helix, and beta-turns in M2 and beta-turns in M3, were observed in the modules at the similar positions to those in the intact barnase but the overall state seems to be in a mixture of random and native conformations. The present result shows that the excised modules have propensity to form similar secondary structures to those of the intact barnase.
蛋白质由诸如球状结构域、二级结构和模块等结构单元组成。模块最初是通过将球状结构域划分为紧密区域来定义的,每个紧密区域都是一个具有紧密构象的连续多肽片段。由于模块与基因的内含子位置密切相关,它们被视为由外显子编码并重新排列的原始多肽片段,从而在早期生物进化中产生它们的新组合。当模块在其边界处被切除时,它们在溶液中是否保持其天然构象?为了找到这个问题的答案,我们合成了细菌核糖核酸酶之一的巴那斯酶的模块,并通过二维核磁共振研究研究了模块M2(氨基酸残基24 - 52)和M3(52 - 73)的溶液结构。在模块中观察到了一些局部二级结构,M2中的α-螺旋和β-转角以及M3中的β-转角,其位置与完整巴那斯酶中的相似,但整体状态似乎处于随机构象和天然构象的混合状态。目前的结果表明,切除的模块倾向于形成与完整巴那斯酶相似的二级结构。