烟酸的三维结构单核苷酸:5、6 - dimethylbenzimidazole phosphoribosyltransferase (CobT)鼠伤寒沙门氏菌和5,1.9 6-dimethybenzimidazole及其反应产物决定决议。
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昌CG Escalante-Semerena JC, Rayment我
烟酸的三维结构单核苷酸:5、6 - dimethylbenzimidazole phosphoribosyltransferase (CobT)鼠伤寒沙门氏菌和5,1.9 6-dimethybenzimidazole及其反应产物决定决议。
生物化学,1999年12月7日,38 (49):16125 - 35。
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10587435 (在PubMed]
- 文摘
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烟酸酯单核苷酸:5,6-dimethylbenzimidazole phosphoribosyltransferase (CobT)鼠伤寒沙门氏菌合成alpha-ribazole过程中扮演着重要的角色,这是一个低配体的钴胺素的重要组成部分。两个x射线结构CobT报告在1.9一项决议。第一,一个复杂的CobT 5 6-dimethylbenzimidazole,第二,烟酸CobT与其反应的一个复杂的产品,和alpha-ribazole-5的磷酸。CobT与5共晶,6-dimethylbenzimidazole (DMB)的空间群P2(1) 2(1) 2 = 72.1的单胞尺寸,b = 90.2 a, c = 47.5每不对称单元和一个原体。随后,水晶含有烟酸DMB浸泡在单核苷酸于是晶格产生的生理反应发生烟酸和alpha-ribazole-5的磷酸。这些研究表明,CobT每个单元包含两个域的二聚体。大域是由一个平行six-strandedβ褶板与连接阿尔法螺旋展览的拓扑罗斯曼褶皱。小域是由组件的N -多肽链的c端部分和包含一个three-helix包。的褶皱CobT无关的I型和II phosphoribosylpyrophosphate依赖转移酶和似乎没有任何其他蛋白质的结构。酶的活性部位位于一个大空腔形成的循环的c端结束beta-strands和邻近单元的小领域。 DMB binds in a hydrophobic pocket created in part by the neighboring small domain. This is consistent with the broad specificity of this enzyme for aromatic substrates [Trzebiatowski, J. R., Escalante-Semerena (1997) J. Biol. Chem. 272, 17662-17667]. The binding site for DMB suggests that Glu317 is the catalytic base required for the reaction. The remainder of the cavity binds the nicotinate and ribose-5'-phosphate moieties, which are nestled within the loops at the ends of the beta-strands. Interestingly, the orientation of the substrate and products are opposite from that expected for a Rossmann fold.