同晶型大肠杆菌二氢叶酸还原酶的晶体结构与叶酸,5-deazafolate,和5,10-dideazatetrahydrofolate:机械的影响。
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雷耶斯VM,莎瓦亚先生,布朗KA,德国人J
同晶型大肠杆菌二氢叶酸还原酶的晶体结构与叶酸,5-deazafolate,和5,10-dideazatetrahydrofolate:机械的影响。
生物化学。1995年2月28日,34(8):2710 - 23所示。
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7873554 (在PubMed]
- 文摘
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晶体结构的大肠杆菌二氢叶酸还原酶(EC 1.5.1.3 ecDHFR)二进制与叶酸复合物,5-deazafolate (5 dfol),和5,10-dideazatetrahydrofolate (ddTHF)精制r个因子为13.7%,14.9%,和14.5%,分别为1.9。所有三个同形与之前报道的二进制复杂ecDHFR与甲氨蝶呤(MTX),在空间群P6(1),每两个分子不对称单位(柏林时,j . T。、Filman d J。马修斯,d。哈姆林,r . C。和德国人,j .(1982)生物。化学,257,13650 - 13662]。一个难以察觉的水分子氢连着蝶啶它们和O4分子不对称单位的叶酸复杂(但不是5 dfol或ddTHF复合物),支持的假设它们被质子化作用的底物,DHFR反应的一个重要步骤,发生这样一个水分子。没有迹象表明之间的氢键N8 Ile-5羰基5 dfol和骨干,这表明细菌酶,与人类酶(戴维斯,j·F。二世,Delcamp t J。,普兰德加斯特:J。阿什福德,诉。Freisheim, j . H。和酸泡菜,j .(1990)生物化学29日9467 - 9479),不支持在N8质子化作用。这也许解释了为什么细菌DHFR比脊椎动物更有效DHFR叶酸含量减少。 When the ecDHFR.NADPH complex (space group P3221; M. R. Sawaya, in preparation) is superimposed on the folate and 5dfol complexes, the distances from pteridine C6 to nicotinamide C4 were found to be 2.9 and 2.8 A, respectively, in close agreement with the theoretically calculated optimal distance in the transition state for hydride transfer [Wu, Y. D., & Houk, K. N. (1987) J. Am. Chem. Soc. 109, 906-908, 2226-2227]. In contrast to the planar ring system of folate or 5dfol, the reduced pteridine ring of ddTHF is severely puckered and bent toward the nicotinamide pocket, with the reduced pyridine ring assuming a half-chair type of conformation. This change in shape causes the pteridine ring to bind with O4 closer to Trp-22(N epsilon 1) by over 0.5 A, so that an invariant water molecule now bridges these two atoms with ideal hydrogen bonds. Furthermore, while the pABA rings of folate and 5dfol are nearly coincident and closer to the alpha C helix than to the alpha B helix, those of MTX and ddTHF are displaced along the binding crevice by approximately 1.1 and 0.6 A, respectively, and are equidistant from alpha B and alpha C.(ABSTRACT TRUNCATED AT 400 WORDS)