Two‐carbon folate cycle of commensalLactobacillus reuteri6475 gives rise to immunomodulatory ethionine, a source for histone ethylation

Abstract

Colonization of the gut by certain probiotic Lactobacillus reuteri strains has been associated with reduced risk of inflammatory diseases and colorectal cancer. Previous studies pointed to a functional link between immunomodulation, histamine production, and folate metabolism, the central 1‐carbon pathway for the transfer of methyl groups. Using mass spectrometry and NMR spectroscopy, we analyzed folate metabolites of L. reuteri strain 6475 and discovered that the bacterium produces a 2‐carbon‐transporting folate in the form of 5, 10‐ethenyl‐tetrahydrofolyl polyglutamate. Isotopic labeling permitted us to trace the source of the 2‐carbon unit back to acetate of the culture medium. We show that the 2C folate cycle of L. reuteri is capable of transferring 2 carbon atoms to homocysteine to generate the unconventional amino acid ethionine, a known immunomodulator. When we treated monocytic THP‐1 cells with ethionine, their transcription of TNF‐α was inhibited and cell proliferation reduced. Mass spectrometry of THP‐1 histones revealed incorporation of ethionine instead of methionine into proteins, a reduction of histone‐methylation, and ethylation of histone lysine residues. Our findings suggest that the microbiome can expose the host to ethionine through a novel 2‐carbon transporting variant of the folate cycle and modify human chromatin via ethylation.—Roth, D., Chiang, A. J., Hu, W., Gugiu, G. B., Morra, C. N., Versalovic, J., Kalkum, M. The two‐carbon folate cycle of commensal Lactobacillus reuteri 6475 gives rise to immunomodulatory ethionine, a source for histone ethylation. FASEB J. 33,3536‐3548 (2019). http://www.fasebj.org

Complex Responses to Hydrogen Peroxide and Hypochlorous Acid by the Probiotic Bacterium Lactobacillus reuteri

“…Lactobacillus reuteri is a well-established model probiotic bacterium that is able to stably colonize the mammalian intestine (32, 33), where several strains have been shown to combat inflammation and enteric infections by different mechanisms, including anti-inflammatory histamine synthesis by strains ATCC PTA 6475 and ATCC PTA 5289 (34–37), modulation of immune cell functions by strains ATCC PTA 6475, 100-23, and WU (33, 38–40), and production of antimicrobial compounds (e.g., reuterin and reutericyclin) by ATCC PTA 6475 and many other strains (37, 41, 42). While the genome-wide stress responses of L.…”

Microbial Metabolic Capacity for Intestinal Folate Production and Modulation of Host Folate Receptors

“…In contrast, folates synthesized by L. reuteri 6475 produce relatively long glutamate tails (FPGs; chain length 7–9 glutamate residues), which increase in length by adding glutamate residues over time (Figure 3D). In addition, to the simple 5,10-methenyl THF (tetrahydrofolic acid) polyglutamate polymers produced by E. coli Nissle 1917, L. reuteri 6475 produces both 5,10-methenyl THF polyglutamates and a unique 5,10−ethenyl THF with a covalently linked γ-polyglutamate tail (Roth et al, 2019). 5,10-Ethenyl THF carries two carbons at the “business end” of THF, between N5 and N10.…”

“…5,10-Ethenyl THF carries two carbons at the “business end” of THF, between N5 and N10. It contributes to a two-carbon variant of the folate cycle that leads to the production of ethionine instead of methionine (Roth et al, 2019). These data are among the first to identify commensal gut microbes with unique patterns of glutamylated folate, which may have an impact on host folate processes.…”

Microbial Metabolites in Colorectal Cancer: Basic and Clinical Implications

“…Liquid chromatography-mass spectrometry (LC-MS) is even more widely used for the analysis of both non-polar metabolites (bile acids, lipids) [ 27 ] and polar metabolites (vitamins and their derivatives, amino acids, etc.) [ 28 ]. LC-MS employs softer ionization and lower temperature than GC-MS, making it more suitable for larger, non-volatile and less stable metabolites.…”