Peterson D L, Gleisner J M, Blakley R L
J Biol Chem. 1975 Jul 10;250(13):4945-54.
The complete amino acid sequence of the mutant dihydrofolate reductase from Streptococcus faecium var. Durans strain A has been determined by sequence analysis of peptides produced by tryptic, chymotryptic, thermolytic, and mild acid cleavage of the large peptide CNBr 7 and from previously reported studies. The sequence of the S. faecium enzyme is compared to the reported sequence of dihydrofolate reductase from Escherichia coli and the two are shown to contain two domains of substantial homology. One of these domains consists of the NH2-terminal 60 residues and is considered to contribute the dihydrofolate binding site. The second domain probably contains the dinucleotide binding structure. Comparison of the sequences of the dihydrofolate reductases with those of larger dehydrogenases of known structure failed to show any evidence for homology. Considerations of size and predictions of secondary structure also suggest that the second domain in the reductases has no structural similarity to the nucleotide binding site in the larger dehydrogenases. It is concluded that the two reductases are related, although distantly, but that they have evolved from an ancestral protein different from the primitive predecessor of the other oxidoreductases.
通过对大肽CNBr 7经胰蛋白酶、胰凝乳蛋白酶、嗜热菌蛋白酶和温和酸裂解产生的肽段进行序列分析，并结合先前报道的研究，已确定了来自粪肠球菌变种杜兰菌株A的突变二氢叶酸还原酶的完整氨基酸序列。将粪肠球菌酶的序列与已报道的大肠杆菌二氢叶酸还原酶序列进行比较，结果表明二者含有两个具有显著同源性的结构域。其中一个结构域由氨基末端的60个残基组成，被认为构成了二氢叶酸结合位点。第二个结构域可能包含二核苷酸结合结构。将二氢叶酸还原酶的序列与已知结构的较大脱氢酶的序列进行比较，未发现任何同源性证据。对大小的考量和二级结构的预测也表明，还原酶中的第二个结构域与较大脱氢酶中的核苷酸结合位点没有结构相似性。结论是，这两种还原酶虽然关系较远，但它们是从一种不同于其他氧化还原酶原始前身的祖先蛋白进化而来的。
