Kuribayashi Taka-Aki, Fujii Sotaro, Masanari Misa, Yamanaka Masaru, Wakai Satoshi, Sambongi Yoshihiro
Graduate School of Biosphere Science, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima, Hiroshima, 739-8528, Japan.
Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara, 630-0192, Japan.
Extremophiles. 2017 Mar;21(2):357-368. doi: 10.1007/s00792-016-0909-8. Epub 2017 Jan 3.
Shewanella species are widely distributed in sea, brackish, and fresh water areas, growing psychrophilically or mesophilically, and piezophilically or piezo-sensitively. Here, membrane-bound 5'-nucleotidases (NTases) from deep-sea Shewanella violacea and brackish water Shewanella amazonensis were examined from the aspect of NaCl tolerance to gain an insight into protein stability against salt. Both NTases were single polypeptides with molecular masses of ~59 kDa, as determined on mass spectroscopy. They similarly required 10 mM MgCl for their activities, and they exhibited the same pH dependency and substrate specificity for 5'-nucleotides. However, S. violacea 5'-nucleotidase (SVNTase) was active enough in the presence of 2.5 M NaCl, whereas S. amazonensis 5'-nucleotidase (SANTase) exhibited significantly reduced activity with the same concentration of the salt. Although SVNTase and SANTase exhibited high sequence identity (69.7%), differences in the ratio of acidic to basic amino acid residues and the number of potential salt bridges maybe being responsible for the difference in the protein stability against salt. 5'-Nucleotidases from these Shewanella species will provide useful information regarding NaCl tolerance, which may be fundamental for understanding bacterial adaptation to growth environments.
希瓦氏菌属广泛分布于海洋、咸淡水和淡水区域，可在嗜冷或嗜温条件下生长，也可在嗜压或对压力敏感的条件下生长。在此，从耐NaCl方面对深海紫色希瓦氏菌和咸水亚马逊希瓦氏菌的膜结合5'-核苷酸酶（NTases）进行了研究，以深入了解蛋白质对盐的稳定性。质谱分析确定，这两种NTases均为单链多肽，分子量约为59 kDa。它们的活性同样需要10 mM MgCl，并且对5'-核苷酸表现出相同的pH依赖性和底物特异性。然而，紫色希瓦氏菌5'-核苷酸酶（SVNTase）在2.5 M NaCl存在下仍具有足够的活性，而亚马逊希瓦氏菌5'-核苷酸酶（SANTase）在相同盐浓度下活性显著降低。尽管SVNTase和SANTase表现出较高的序列同一性（69.7%），但酸性与碱性氨基酸残基的比例以及潜在盐桥数量的差异可能是导致蛋白质对盐稳定性不同的原因。这些希瓦氏菌属的5'-核苷酸酶将为耐NaCl性提供有用信息，这对于理解细菌对生长环境的适应性可能至关重要。
