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結構導向功能：克雷伯氏肺炎桿菌中之碲酸鹽抗藥蛋白之核磁共振研究

為了解決unix離子夾的問題，作者潘韻如 這樣論述：

Ter proteins mediate tellurite resistance and other responses to extracellular stimuli, but their functions are not understood yet. To shed light into the function of KP-TerD, a 20.5 kDa tellurite resistance protein from a plasmid of Klebsiella pneumoniae, we solved its three-dimensional structure

in solution by multidimensional NMR spectroscopy. The structure consists of a beta-sandwich formed by two five-stranded beta-sheets and six short helices. Interestingly, the structure contains two clusters of negatively charged residues, which suggested that KP-TerD might bind some metal ions. Usin

g NMR, CD and ICP-OES, we demonstrate that KP-TerD binds two calcium ions. An EDTA competition assay monitored by 1D NMR spectroscopy showed the estimated dissociation constants of KP-TerD. Since the Ca2+ concentration in the cytoplasm of bacteria is estimated to be 90-300 nM, the estimated Kd of si

te Ca2 of KP-TerD (200 nM) is well suited to sense changes in the cytoplasmic Ca2+ concentrations of bacteria. The calcium ligands are highly conserved in TerD proteins, suggesting that calcium binding is a conserved property of this family. Moreover, the calcium-binding motif of KP-TerD is conserve

d in TerE and TerZ. Using analogous methodology, we show that KP-TerE and KP-TerZ also bind two calcium ions, but their affinties are different from KP-TerD. These results show that three out of seven Ter proteins bind calcium and their affinities cover a wide range (from ?嵱 to nM) that is ideal to

respond to changes in cytoplasmic calcium concentration. Overall, these data suggest that TerD, TerE and TerZ function as calcium sensors and that some form of calcium signaling is critical for the Ter response to extracellular stimuli.