Difference in NaCl tolerance of membrane-bound 5′-nucleotidases purified from deep-sea and brackish water Shewanella species
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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 in order 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 MgCl2 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.
This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan [No. 26240045], a grant from the Japan Society for the Promotion of Science [No. 25-1446], and The Salt Science Research Foundation [No. 1655].
This is a post-peer-review, pre-copyedit version of an article published in Extremophiles. The final authenticated version is available online at: https://doi.org/10.1007/s00792-016-0909-8