期刊
INTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES
卷 159, 期 -, 页码 517-529出版社
ELSEVIER
DOI: 10.1016/j.ijbiomac.2020.05.081
关键词
Serine hydroxymethyltransferase; Aphanothece halophytica; Salt tolerance
资金
- Sapienza (Progetto di Ateneo)
- Istituto Pasteur Italia -Fondazione Cenci Bolognetti
- NCI, Center for Cancer Research
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [W-31-109-Eng-38]
Serine hydroxymethyltransferase (SHMT) is a pyridoxal 5'-phosphate-dependent enzyme that plays a pivotal role in cellular one-carbon metabolism. In plants and cyanobacteria, this enzyme is also involved in photorespiration and confers salt tolerance, as in the case of SHMT from the halophilic cyanobacterium Aphanothece halophytica (AhSHMT). We have characterized the catalytic properties of AhSHMT in different salt and pH conditions. Although the kinetic properties of AhSHMT correlate with those of the mesophilic orthologue from Escherichia coli, AhSHMT appears more catalytically efficient, especially in presence of salt. Our studies also reveal substrate inhibition, previously unobserved in AhSHMT. Furthermore, addition of the osmoprotectant glycine betaine under salt conditions has a distinct positive effect on AhSHMT activity. The crystal structures of AhSHMT in three forms, as internal aldimine, as external aldimine with the L-serine substrate, and as a covalent complex with malonate, give structural insights on the possible role of specific amino acid residues implicated in the halophilic features of AhSHMT. Importantly, we observed that overexpression of the gene encoding SHMT, independently from its origin, increases the capability of E. coli to grow in high salt conditions, suggesting that the catalytic activity of this enzyme in itself plays a fundamental role in salt tolerance. (C) 2020 Elsevier B.V. All rights reserved.
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