An alternative menaquinone biosynthetic pathway operating in microorganisms: an attractive target for drug discovery to pathogenic Helicobacter and Chlamydia strains

Abstract

Menaquinone is an essential vitamin as an obligatory component of the electron transfer pathway in microorganisms. Menaquinone has been shown to be derived from chorismate by eight enzymes, designated MenA to -H in Escherichia coli. However, bioinformatic analyses of whole-genome sequences have suggested that some microorganisms, such as Helicobacter pylori and Campylobacter jejuni, which are known to cause gastric carcinoma and diarrhea, respectively, do not have orthologs of most of the men genes, although they synthesize menaquinone. The 13 C-labeling pattern of menaquinone purified from Streptomyces coelicolor A3(2) grown on [U-13 C]glucose was quite different from that of E. coli, suggesting that an alternative pathway was operating in the strain. We searched for candidate genes participating in the alternative pathway by in silico screening, and the involvement of these genes in the pathway was confirmed by gene-disruption experiments. We also used mutagenesis to isolate mutants that required menaquinone for their growth and used these mutants as hosts for shotgun cloning experiments. Metabolites that accumulated in the culture broth of mutants were isolated and their structures were determined. Taking these results together, we deduced the outline of the alternative pathway, which branched at chorismate in a similar manner to the known pathway but then followed a completely different pathway. As humans and some useful intestinal bacteria, such as lactobacilli, lack the alternative pathway, it would be an attractive target for the development of chemotherapeutics.

5′-Methylthioadenosine Nucleosidase Is Implicated in Playing a Key Role in a Modified Futalosine Pathway for Menaquinone Biosynthesis in Campylobacter jejuni

“…In 2005, it was reported that various Streptomyces species lack orthologs of the menB--menF genes (12), suggesting that an entirely unique biosynthetic pathway is operative in these organisms. Interestingly, these genes are also absent in the pathogenic bacteria C. jejuni and H. pylori, even though these organisms are known to biosynthesize menaquinone (9). Isotopic feeding studies confirmed that a unique pathway is employed in Streptomyces, and 1,4-dihydroxy-6-naphthoate (DHN) was implicated as an intermediate (see Fig.…”

“…Bioinformatic analysis strongly implied that the futalosine pathway is also operative in the pathogenic organisms C. jejuni and H. pylori (9,14). These bacteria lack homologs to the men genes of E. coli and possess homologs to the mqn genes of S. coelicolor.…”

“…H. pylori causes gastritis that can lead to peptic ulceration and gastric cancer (18). Because these bacteria require menaquinone biosynthesis for survival and because they use a biosynthetic pathway that differs from that employed by other beneficial intestinal microbiota such as lactobacilli, these enzymes represent attractive targets for the development of specific antibacterial compounds that may exhibit minimal adverse side effects (2,9).…”

“…In these organisms, menaquinone is required for survival. Because humans are unable to synthesize menaquinone, the bacterial enzymes responsible for the biosynthesis of this vitamin serve as viable targets for the development of antibacterial compounds (2,9).…”

Structural and Biochemical Characterization of Chlamydia trachomatis Hypothetical Protein CT263 Supports That Menaquinone Synthesis Occurs through the Futalosine Pathway

“…E. coli) utilize the traditional route. The absence of futalosine genes in these organisms strengthens the development of antimicrobial compounds targeting pathogenic bacteria that synthesize MK (8).…”