Noguti T, Sakakibara H, Go M
Department of Biology, Faculty of Science, Nagoya University, Japan.
Proteins. 1993 Aug;16(4):357-63. doi: 10.1002/prot.340160405.
Proteins in eukaryotes are composed of structural units, each encoded by discrete exons. The protein module is one such structural unit; it has been defined as the least extended or the most compact contiguous segment in a globular domain. To elucidate roles of modules in protein evolution and folding, we examined roles of hydrogen bonds and hydrophobic cores, as related to the stability of these modules. For this purpose we studied barnase, a bacterial RNase from Bacillus amylolique-faciens. Barnase is decomposed into at least six modules, M1-M6; the module boundaries are identified at amino acid residues 24, 52, 73, 88, and 98. Hydrogen bonds are localized mainly within each of the modules, with only a few between them, thereby indicating that their locations are designed to primarily stabilize each individual module. To obtain support for this notion, an analysis was made of hypothetical modules defined as segments starting at a center of one module and ending at the center of the following one. We found that the hydrogen bonds did not localize in each hypothetical module and that many formed between the hypothetical modules. The native conformations of modules of barnase may be specified predominantly by interactions within the modules.
真核生物中的蛋白质由结构单元组成，每个结构单元由离散的外显子编码。蛋白质模块就是这样一种结构单元；它被定义为球状结构域中延伸最少或最紧密的连续片段。为了阐明模块在蛋白质进化和折叠中的作用，我们研究了与这些模块稳定性相关的氢键和疏水核心的作用。为此，我们研究了芽孢杆菌核糖核酸酶（barnase），一种来自解淀粉芽孢杆菌的细菌核糖核酸酶。芽孢杆菌核糖核酸酶可分解为至少六个模块，M1 - M6；模块边界在氨基酸残基24、52、73、88和98处确定。氢键主要位于每个模块内部，它们之间只有少数几个，这表明氢键的位置主要是为了稳定每个单独的模块。为了支持这一观点，我们对假设模块进行了分析，这些假设模块被定义为从一个模块的中心开始到下一个模块的中心结束的片段。我们发现氢键并不定位于每个假设模块内，而且许多氢键在假设模块之间形成。芽孢杆菌核糖核酸酶模块的天然构象可能主要由模块内的相互作用决定。
