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首页> 外文期刊>Journal of Molecular Biology >The structure of the membrane protein squalene-hopene cyclase at 2.0 A resolution.
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The structure of the membrane protein squalene-hopene cyclase at 2.0 A resolution.

机译：膜蛋白角鲨烯-戊环化酶的结构分辨率为2.0A。

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摘要

Squalene cyclases catalyze a cationic cyclization cascade, which is homologous to a key step in cholesterol biosynthesis. The structure of the enzyme from Alicyclobacillus acidocaldarius has been determined in a new crystal form at 2.0 A resolution (1 A=0.1 nm) and refined to an R-factor of 15.3 % (Rfree=18.7 %). The structure indicates how the initial protonation and the final deprotonation of squalene occur and how the transient carbocations are stabilized. The pathways of the flexible educt squalene from the membrane interior to the active center cavity and of the rigid fused-ring product hopene in the reverse direction are discussed. The enzyme contains eight so-called QW-sequence repeats that fortify the alpha/alpha-barrels by an intricate interaction network. They are unique to the known triterpene cyclases and are presumed to shield these enzymes against the released enthalpy of the highly exergonic catalyzed reaction. The enzyme is a monotopic membrane protein, the membrane-binding interactions of which are described and compared with those of two prostaglandin-H2 synthase isoenzymes, the only other structurally characterized proteins of this type. In the crystals the membrane-binding regions face each other, suggesting a micelle-type detergent structure between them. Copyright 1999 Academic Press.
机译：角鲨烯环化酶催化阳离子环化级联反应，与胆固醇生物合成的关键步骤同源。来自酸热脂环酸杆菌的酶的结构已经以2.0 A的分辨率（1 A = 0.1 nm）以新的晶体形式确定，并精炼到15.3％的R因子（Rfree = 18.7％）。该结构表明角鲨烯的初始质子化和最终去质子化如何发生，以及瞬态碳正离子如何稳定。讨论了柔性离析物角鲨烯从膜内部到活动中心腔的路径以及刚性稠环产物hopene在相反方向上的路径。该酶包含八个所谓的QW序列重复序列，这些序列通过复杂的相互作用网络加强了alpha / alpha桶。它们是已知的三萜环化酶所特有的，并被认为可以保护这些酶免受高能催化反应释放的焓的影响。该酶是一种单分子膜蛋白，其膜结合相互作用已被描述并与两种前列腺素-H2合酶同工酶（它们是这种结构中唯一的其他蛋白）进行了比较。在晶体中，膜结合区彼此面对，表明它们之间具有胶束型洗涤剂结构。版权所有1999，学术出版社。

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