Chu Chen-Hsi, Liu Mu-Hsuan, Chen Pin-Chen, Lin Ming-Hsing, Li Yi-Chuan, Hsiao Chwan-Deng, Sun Yuh-Ju
Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu 300, Taiwan.
Acta Crystallogr D Biol Crystallogr. 2012 Jul;68(Pt 7):773-83. doi: 10.1107/S0907444912011407. Epub 2012 Jun 15.
Uridylate kinase (UMPK; EC 2.7.4.22) transfers the γ-phosphate of ATP to UMP, forming UDP. It is allosterically regulated by GTP. Structures of Helicobacter pylori UMPK (HpUMPK) complexed with GTP (HpUMPK-GTP) and with UDP (HpUMPK-UDP) were determined at 1.8 and 2.5 Å resolution, respectively. As expected, HpUMPK-GTP forms a hexamer with six GTP molecules at its centre. Interactions between HpUMPK and GTP are made by the β3 strand of the sheet, loop β3α4 and the α4 helix. In HpUMPK-UDP, the hexameric symmetry typical of UMPKs is absent. Only four of the HpUMPK molecules bind UDP; the other two HpUMPK molecules are in the UDP-free state. The asymmetric hexamer of HpUMPK-UDP, which has an exposed dimer interface, may assist in UDP release. Furthermore, the flexibility of the α2 helix, which interacts with UDP, is found to increase when UDP is absent in HpUMPK-UDP. In HpUMPK-GTP, the α2 helix is too flexible to be observed. This suggests that GTP binding may affect the conformation of the α2 helix, thereby promoting UDP release.
尿苷酸激酶（UMPK；EC 2.7.4.22）将ATP的γ-磷酸基团转移至UMP上，形成UDP。它受到GTP的变构调节。分别在1.8 Å和2.5 Å分辨率下测定了与GTP结合的幽门螺杆菌UMPK（HpUMPK-GTP）以及与UDP结合的HpUMPK（HpUMPK-UDP）的结构。正如预期的那样，HpUMPK-GTP形成六聚体，其中心有六个GTP分子。HpUMPK与GTP之间的相互作用由片层的β3链、环β3α4和α4螺旋介导。在HpUMPK-UDP中，不存在UMPK典型的六聚体对称性。只有四个HpUMPK分子结合UDP；另外两个HpUMPK分子处于无UDP状态。具有暴露二聚体界面的HpUMPK-UDP不对称六聚体可能有助于UDP的释放。此外，发现与UDP相互作用的α2螺旋在HpUMPK-UDP中不存在UDP时灵活性增加。在HpUMPK-GTP中，α2螺旋过于灵活而无法观察到。这表明GTP结合可能影响α2螺旋的构象，从而促进UDP的释放。
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