6ymf
Crystal structure of serine hydroxymethyltransferase from Aphanothece halophytica in the PLP-Serine external aldimine state
Structural highlights
FunctionI7H6W6_APHHA Catalyzes the reversible interconversion of serine and glycine with tetrahydrofolate (THF) serving as the one-carbon carrier. This reaction serves as the major source of one-carbon groups required for the biosynthesis of purines, thymidylate, methionine, and other important biomolecules. Also exhibits THF-independent aldolase activity toward beta-hydroxyamino acids, producing glycine and aldehydes, via a retro-aldol mechanism.[HAMAP-Rule:MF_00051] Publication Abstract from PubMedSerine hydroxymethyltransferase (SHMT) is a pyridoxal 5'-phosphate-dependent enzyme that plays a pivotal role in cellular onecarbon 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. Structural and kinetic properties of serine hydroxymethyltransferase from the halophytic cyanobacterium Aphanothece halophytica provide a rationale for salt tolerance.,Nogues I, Tramonti A, Angelaccio S, Ruszkowski M, Sekula B, Contestabile R Int J Biol Macromol. 2020 May 15;159:517-529. doi:, 10.1016/j.ijbiomac.2020.05.081. PMID:32417544[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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