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首页> 外文期刊>Acta crystallographica.Section D. Biological crystallography >The effect of heavy atoms on the conformation of the active-site polypeptide loop in human ABO(H) blood-group glycosyltransferase B
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The effect of heavy atoms on the conformation of the active-site polypeptide loop in human ABO(H) blood-group glycosyltransferase B

机译：重原子的构象的影响活性部位多肽循环在人类ABO血型(H)B血型糖基转移酶

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The human ABO(H) blood-group antigens are oligosaccharide structures that are expressed on erythrocyte and other cell surfaces. The terminal carbohydrate residue differs between the blood types and determines the immune reactivity of this antigen. Individuals with blood type A have a terminal N-acetylgalactosamine residue and those with blood type B have a terminal galactose residue. The attachment of these terminal carbohydrates are catalyzed by two different glycosyltransferases: an (13)N-acetylgalactosaminyltransferase (GTA) and an (13)galactosyltransferase (GTB) for blood types A and B, respectively. GTA and GTB are homologous enzymes that differ in only four of 354 amino-acid residues (Arg/Gly176, Gly/Ser235, Leu/Met266 and Gly/Ala268 in GTA and GTB, respectively). Diffraction-quality crystals of GTA and GTB have previously been grown from as little as 10 mg ml-1 stock solutions in the presence of Hg, while diffraction-quality crystals of the native enzymes require much higher concentrations of protein. The structure of a single mutant C209A has been determined in the presence and absence of heavy atoms and reveals that when mercury is complexed with Cys209 it forces a significant level of disorder in a polypeptide loop (amino acids 179-195) that is known to cover the active site of the enzyme. The observation that the more highly disordered structure is more amenable to crystallization is surprising and the derivative provides insight into the mobility of this polypeptide loop compared with homologous enzymes.
机译：人类的ABO血型(H)血型抗原低聚糖结构表达红细胞和其他细胞表面。碳水化合物残留血液之间的不同类型和确定的免疫反应性这种抗原。一个终端和N-acetylgalactosamine残渣那些血液B型终端半乳糖残渣。碳水化合物是由两种不同的催化糖基转移酶:(13) N-acetylgalactosaminyltransferase (GTA)和(13)半乳糖基转移酶(GTB)血分别类型A和B。同源的只有四个不同的酶354氨基酸残基(Arg / Gly176 g / Ser235,低浓缩铀/ Met266和g / Ala268侠盗猎车手和GTB分别)。侠盗猎车手和GTB此前从增长10毫克ml-1股票的解决方案Hg的存在,而diffraction-quality晶体的原生酶需要太多更高的蛋白质含量。一个突变C209A已经确定的存在和缺乏重原子和表明,当水星是包裹着Cys209它强迫障碍的显著水平氨基酸多肽循环(179 - 195)众所周知,酶的活性部位。观察高度无序结构更易于结晶令人惊讶的和导数提供洞察力这种多肽循环的流动相比之下,同源酶。

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