嘌呤核苷磷酸化酶的晶体结构(PNP)纤维菌属sp.及其机制的含义三聚物的PNP型。
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Tebbe J, Bzowska Wielgus-Kutrowska B,施罗德W, Kazimierczuk Z, Shugar D, Saenger W, Koellner G
嘌呤核苷磷酸化酶的晶体结构(PNP)纤维菌属sp.及其机制的含义三聚物的PNP型。
J杂志。1999年12月17日,294 (5):1239 - 55。
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10600382 (在PubMed]
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三聚物的嘌呤核苷磷酸化酶的三维结构(PNP)纤维菌属sp.已经由x射线晶体学。二进制复杂的酶与正磷酸盐结晶的斜方晶系的空间群P212121单位细胞尺寸= 64.1,b = 108.9 a, c = 119.3,保持酶的活性三聚物的不对称单元。x射线数据收集在4摄氏度使用同步辐射(EMBL /谜底,汉堡)。分子结构是解决替换,小腿脾PNP型结构模型,和精制2.2决议。“终端”三元复杂的酶与正磷酸盐和8-iodoguanine被浸泡了晶体的二进制正磷酸盐复杂衬底8-iodoguanosine非常薄弱。数据被收集在100 K CuKalpha辐射,和三维结构细化2.4决议。虽然纤维菌属的顺序PNP型股票只有33%的身份与小牛脾酶,和几乎没有身份hexameric大肠杆菌PNP型,所有三个酶有许多共同的结构特点,viz. nine-stranded中央β褶板,活动中心的位置,配体的几何布置在活动中心。周围的螺旋也盛行的一些相似之处。在纤维菌属PNP、三种活性中心每三聚物被正磷酸盐,正磷酸盐和基础,分别和小单体之间的结构差异,B和C。这支持子单元之间的协同(non-identity绑定网站),而不是每个单体存在多个结合位点,正如前面建议绑定磷酸的哺乳动物pnp型。 The phosphate binding site is located between two conserved beta- and gamma-turns and consists of Ser46, Arg103, His105, Gly135 and Ser223, and one or two water molecules. The guanine base is recognized by a zig-zag pattern of possible hydrogen bonds, as follows: guanine N-1...Glu204 O(epsilon1)...guanine NH2...Glu204 O(epsilon2). The exocyclic O6 of the base is bridged via a water molecule to Asn246 N(delta), which accounts for the inhibitory, but lack of substrate, activity of adenosine. An alternative molecular mechanism for catalysis by trimeric PNPs is proposed, in which the key catalytic role is played by Glu204 (Glu201 in the calf and human enzymes), while Asn246 (Asn243 in the mammalian enzymes) supports binding of 6-oxopurines rather than catalysis. This mechanism, in contrast to that previously suggested, is consistent with the excellent substrate properties of N-7 substituted nucleosides, the specificity of trimeric PNPs versus 6-oxopurine nucleosides and the reported kinetic properties of Glu201/Ala and Asn243/Ala point variants of human PNP.