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首页> 外文期刊>Acta crystallographica.Section D. Biological crystallography >Monoclinic guanidinoacetate methyltransferase and gadolinium ion-binding characteristics.
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Monoclinic guanidinoacetate methyltransferase and gadolinium ion-binding characteristics.

机译：单斜guanidinoacetate甲基转移酶和钆ion-binding特征。

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摘要

Guanidinoacetate methyltransferase (GAMT) is the enzyme that catalyzes the last step of creatine biosynthesis. The enzyme is found in abundance in the livers of all vertebrates. Recombinant rat liver GAMT truncated at amino acid 37 from the N-terminus has been crystallized with S-adenosylhomocysteine (SAH) in a monoclinic modification and the crystal structure has been determined at 2.8 A resolution. There are two dimers in the crystallographic asymmetric unit. Each dimer has non-crystallographic twofold symmetry and is related to the other dimer by pseudo-4(3) symmetry along the crystallographic b axis. The overall structure of GAMT crystallized in the monoclinic modification is quite similar to the structure observed in the tetragonal modification [Komoto et al. (2002), J. Mol. Biol. 320, 223-235], with the exception of the loop containing Tyr136. In the monoclinic modification, the loops in three of the four subunits have a catalytically unfavorable conformation and the loop of the fourth subunit has a catalytically favorable conformation as observed in the crystals of the tetragonal modification. From the structures in the monoclinic and tetragonal modifications, we can explain why the Y136F mutant enzyme retains considerable catalytic activity while the Y136V mutant enzyme loses the catalytic activity. The crystal structure of a Gd derivative of the tetragonal modification has also been determined. By comparing the Gd-derivative structure with the native structures in the tetragonal and the monoclinic modifications, useful characteristic features of Gd-ion binding for application in protein crystallography have been observed. Gd ions can bind to proteins without changing the native protein structures and Gd atoms produce strong anomalous dispersion signals from Cu Kalpha radiation; however, Gd-ion binding to protein requires a relatively specific geometry.
机译：Guanidinoacetate甲基转移酶(GAMT)酶,催化肌酸的最后一步生物合成。所有的脊椎动物的肝脏。在氨基酸的37肝脏GAMT截断n端结晶了在单斜S-adenosylhomocysteine (SAH)修改和晶体结构2.8决议决定。二聚体的晶体不对称单位。每个二聚体non-crystallographic双重的对称和其他有关二聚体pseudo-4沿着晶体b(3)对称轴。单斜的修改非常相似正方的结构观察修改[Komoto et al。(2002),j·摩尔。杂志。320年,223 - 235],除了循环包含Tyr136。修改,在三四个循环亚基催化地不利第四亚基的构象和循环有催化地有利的构造吗正方的晶体中观察到修改。单斜和正方的修改,我们可以解释为什么Y136F突变酶保留相当大的催化活性而Y136V突变体酶失去催化活性。Gd的导数的晶体结构正方修改也已确定。通过比较与Gd-derivative结构在正方和原生结构单斜的修改,有用的特征Gd-ion绑定应用程序的特性蛋白质晶体学已经被观察到。离子可以绑定到蛋白质而不改变本机蛋白质结构和Gd原子产生强大的反常色散铜的信号Kalpha辐射;蛋白质需要一个相对具体的几何。

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