Biochemical characterization of a homocysteine S-methyltransferase from Leuconostoc suionicum.

Authors

Tadao Oikawa, Nanami Harada, Sumire Hanafusa, Kazuya Yamanaka, Shiro Kato

Published in

Journal of biochemistry. Sep 10, 2026. Epub Sep 10, 2026.

Abstract

We identified and characterized a homocysteine S-methyltransferase (HMT) from the lactic acid bacterium Leuconostoc suionicum LT-38, representing the first characterization of an HMT from lactic acid bacteria. The enzyme exhibited a kcat/Km value of 15.7 mM-1 s-1 toward L-homocysteine. It showed optimal activity at 30 °C and pH 7.5 and remained stable over a broad range of temperatures (30-60 °C) and pH values (5-9). The enzyme accepted both L- and D-homocysteine as methyl acceptors but displayed markedly higher catalytic efficiency toward the L-form (~30-fold). In contrast, L- and D-cysteine were not utilized. Both S-methyl-L-methionine and S-methyl-D-methionine were consumed in reactions containing racemic S-methyl-DL-methionine, and S-adenosyl-L-methionine was also accepted, whereas betaine and related compounds were not utilized. Gel filtration analysis indicated a monomeric structure (~32 kDa). Phylogenetic analysis showed that Ls-HMT clustered with bacterial HMT homologs and was distinct from mammalian BHMT/BHMT2 proteins. Inductively coupled plasma-mass spectrometry revealed approximately one Zn atom per enzyme molecule, and the Zn-depleted apo enzyme showed no detectable activity. These findings support that Ls-HMT is a Zn-dependent HMT with relatively high activity and expand the functional diversity of microbial HMTs.

PMID:
42720554
Bibliographic data and abstract were imported from PubMed on 10 Sep 2026.

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