Doi Nobuhide, Kakukawa Koichi, Oishi Yuko, Yanagawa Hiroshi
Department of Biosciences and Informatics, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
Protein Eng Des Sel. 2005 Jun;18(6):279-84. doi: 10.1093/protein/gzi034. Epub 2005 May 31.
Searching for functional proteins among random-sequence libraries is a major challenge of protein engineering; the difficulties include the poor solubility of many random-sequence proteins. A library in which most of the polypeptides are soluble and stable would therefore be of great benefit. Although modern proteins consist of 20 amino acids, it has been suggested that early proteins evolved from a reduced alphabet. Here, we have constructed a library of random-sequence proteins consisting of only five amino acids, Ala, Gly, Val, Asp and Glu, which are believed to have been the most abundant in the prebiotic environment. Expression and characterization of arbitrarily chosen proteins in the library indicated that five-alphabet random-sequence proteins have higher solubility than do 20-alphabet random-sequence proteins with a similar level of hydrophobicity. The results support the reduced-alphabet hypothesis of the primordial genetic code and should also be helpful in constructing optimized protein libraries for evolutionary protein engineering.
在随机序列文库中寻找功能性蛋白质是蛋白质工程的一项重大挑战；困难包括许多随机序列蛋白质的溶解性较差。因此，一个大多数多肽都可溶且稳定的文库将大有裨益。尽管现代蛋白质由20种氨基酸组成，但有人提出早期蛋白质是从一个简化的氨基酸字母表进化而来的。在这里，我们构建了一个仅由5种氨基酸（丙氨酸、甘氨酸、缬氨酸、天冬氨酸和谷氨酸）组成的随机序列蛋白质文库，据信这5种氨基酸在益生元环境中最为丰富。对文库中任意选择的蛋白质进行表达和表征表明，与具有相似疏水性水平的20字母随机序列蛋白质相比，5字母随机序列蛋白质具有更高的溶解性。这些结果支持了原始遗传密码的简化字母表假说，也应该有助于构建用于进化蛋白质工程的优化蛋白质文库。
