Biosynthesis of meso-lanthionine in Fusobacterium nucleatum

Arch Biochem Biophys. 2023 Jul 15:743:109666. doi: 10.1016/j.abb.2023.109666. Epub 2023 Jun 16.

Abstract

The opportunistic oral pathogen, Fusobacterium nucleatum contains meso-lanthionine as the diaminodicarboxylic acid in the pentapeptide crosslink of the peptidoglycan layer. The diastereomer, l,l-lanthionine is formed by lanthionine synthase, a PLP-dependent enzyme that catalyzes the β-replacement of l-cysteine with a second equivalent of l-cysteine. In this study, we explored possible enzymatic mechanisms for the formation of meso-lanthionine. Our inhibition studies with lanthionine synthase, described herein, revealed that meso-diaminopimelate, a bioisostere of meso-lanthionine, is a more potent inhibitor of lanthionine synthase compared to the diastereomer, l,l-diaminopimelate. These results suggested that lanthionine synthase could also form meso-lanthionine by the β-replacement of l-cysteine with d-cysteine. Through steady-state and pre-steady state kinetic analysis, we confirm that d-cysteine reacts with the ⍺-aminoacylate intermediate with a kon that was 2-3-fold faster and Kd value that was 2-3fold lower compared to l-cysteine. However, given that intracellular levels of d-cysteine levels are assumed to be significantly lower than that of l-cysteine, we also determined if the gene product, FN1732, with low sequence identity to diaminopimelate epimerase could convert l,l-lanthionine to meso-lanthionine. Using diaminopimelate dehydrogenase in a coupled spectrophotometric assay, we show that FN1732 can convert l,l-lanthionine to meso-lanthionine with a kcat of 0.07 ± 0.001 s-1 and a KM of 1.9 ± 0.1 mM. In summary, our results provide two possible enzymatic mechanisms for the biosynthesis of meso-lanthionine in F. nucleatum.

Keywords: 2,6-Diaminopimelic acid; Epimerase; Fusobacterium nucleatum; Peptidoglycan; meso-Lanthionine.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cysteine*
  • Fusobacterium nucleatum*
  • Kinetics
  • Sulfides

Substances

  • lanthionine
  • Cysteine
  • Sulfides