Conformational transitions driven by pyridoxal-5′-phosphate uptake in the psychrophilic Serine hydroxymethyltransferase from Psychromonas ingrahamii
Conformational transitions driven by pyridoxal-5′-phosphate uptake in the psychrophilic Serine hydroxymethyltransferase from Psychromonas ingrahamii
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DOI：
10.1002/prot.24646
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发表时间：
2014-10-01
影响因子：
2.9
通讯作者：
Pascarella, Stefano
中科院分区：
文献类型：
--
作者：
Angelaccio, Sebastiana;Dworkowski, Florian;Pascarella, Stefano
丝氨酸羟甲基转移酶（Serine hydroxymethyltransferase，SHMT）是一种依赖于吡哆醛-5 '-磷酸（pyridoxal-5'-phosphate，PLP）的酶，属于折叠I型超家族，在体内催化L-丝氨酸和四氢蝶酰谷氨酸（tetrahydropteroylglutamate，H（4）PteGlu）可逆转化为甘氨酸和5，10-亚甲基四氢蝶酰谷氨酸（5，10-CH 2-H（4）PteGlu）。最近从嗜冷细菌Psychromonas ingrahamii（piSHMT）中分离纯化并鉴定了SHMT。该酶显示出典型的嗜冷酶的催化和稳定性质，即在低温下的高催化活性和热不稳定性。为了更深入地了解piSHMT的结构-功能关系，通过X射线晶体学确定其apo形式的三维结构。应用同源建模技术来构建piSHMT全息形式的模型。两种形式的比较揭示了当载脂蛋白酶结合其辅因子时发生的构象改变。我们的研究结果表明，载脂蛋白的形式是在一个“开放”的构象，并拥有四个（或五个，在链A）无序的循环，其电子密度是不可见的X-射线晶体学。这些环含有与PLP辅因子相互作用的残基，其中三个位于主要结构域，沿着小结构域，构成SHMT同二聚体的单个亚基。辅因子结合触发小结构域的重排，其向大结构域移动并在溶剂侧筛选PLP结合位点。与来自鼠伤寒沙门氏菌的嗜温性apo SHMT的比较表明，在嗜冷性SHMT（C）2014 Wiley Periodicals，Inc.
Serine hydroxymethyltransferase (SHMT) is a pyridoxal-5'-phosphate (PLP)-dependent enzyme belonging to the fold type I superfamily, which catalyzes in vivo the reversible conversion of L-serine and tetrahydropteroylglutamate (H(4)PteGlu) to glycine and 5,10-methylenetetrahydropteroylglutamate (5,10-CH2-H(4)PteGlu). The SHMT from the psychrophilic bacterium Psychromonas ingrahamii (piSHMT) had been recently purified and characterized. This enzyme was shown to display catalytic and stability properties typical of psychrophilic enzymes, namely high catalytic activity at low temperature and thermolability. To gain deeper insights into the structure-function relationship of piSHMT, the three-dimensional structure of its apo form was determined by X-ray crystallography. Homology modeling techniques were applied to build a model of the piSHMT holo form. Comparison of the two forms unraveled the conformation modifications that take place when the apo enzyme binds its cofactor. Our results show that the apo form is in an "open" conformation and possesses four (or five, in chain A) disordered loops whose electron density is not visible by X-ray crystallography. These loops contain residues that interact with the PLP cofactor and three of them are localized in the major domain that, along with the small domain, constitutes the single subunit of the SHMT homodimer. Cofactor binding triggers a rearrangement of the small domain that moves toward the large domain and screens the PLP binding site at the solvent side. Comparison to the mesophilic apo SHMT from Salmonella typhimurium suggests that the backbone conformational changes are wider in psychrophilic SHMT (C) 2014 Wiley Periodicals, Inc.