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

Abstract

Menaquinone (vitamin K 2 ) serves as an electron carrier in the electron transport chain required for respiration in many pathogenic bacteria. Most bacteria utilize a common menaquinone biosynthetic pathway as exemplified by Escherichia coli. Recently, a novel biosynthetic pathway, the futalosine pathway, was discovered in Streptomyces. Bioinformatic analysis strongly suggests that this pathway is also operative in the human pathogens Campylobacter jejuni and Helicobacter pylori. Here, we provide compelling evidence that a modified futalosine pathway is operative in C. jejuni and that it utilizes 6-amino-6-deoxyfutalosine instead of futalosine. A key step in the Streptomyces pathway involves a nucleosidase called futalosine hydrolase. The closest homolog in C. jejuni has been annotated as a 5-methylthioadenosine nucleosidase (MTAN). We have shown that this C. jejuni enzyme has MTAN activity but negligible futalosine hydrolase activity. However, the C. jejuni MTAN is able to hydrolyze 6-amino-6-deoxyfutalosine at a rate comparable with that of its known substrates. This suggests that the adeninecontaining version of futalosine is the true biosynthetic intermediate in this organism. To demonstrate this in vivo, we constructed a C. jejuni mutant strain deleted for mqnA2, which is predicted to encode for the enzyme required to synthesize 6-amino-6-deoxyfutalosine. Growth of this mutant was readily rescued by the addition of 6-amino-6-deoxyfutalosine, but not futalosine. This provides the first direct evidence that a modified futalosine pathway is operative in C. jejuni. It also highlights the tremendous versatility of the C. jejuni MTAN, which plays key roles in S-adenosylmethionine recycling, the biosynthesis of autoinducer molecules, and the biosynthesis of menaquinone.

Immucillins in Infectious Diseases

“…A report in 2008 indicated that several bacterial species do not possess homologues of men B to men F and thus must encode a distinct pathway for menaquinone biosynthesis. 10 Subsequent genetic and biochemical analysis indicated an alternative menaquinone synthetic pathway involving the mqn genes with deoxyfutalosine or 6-amino-6-deoxyfutalosine as intermediates (Figure 7) 11,12 . These intermediates are processed by a purine nucleoside hydrolase with homology to other bacterial 5′-methylthioadenosine nucleosidases (MTANs).…”

“…These intermediates are processed by a purine nucleoside hydrolase with homology to other bacterial 5′-methylthioadenosine nucleosidases (MTANs). 11,45 Tansition state analogue design work on pathways of quorum sensing in Gram-negative bacteria had already targeted MTAN to produce powerful inhibitors with dissociation constants as low as 47 fM. 46–48 These were immediate candidates for the H. pylori MTAN.…”

Novel Drug Targets for Food-Borne PathogenCampylobacter jejuni: An Integrated Subtractive Genomics and Comparative Metabolic Pathway Study

“…5¢-Methylthioadenosine/S-adenosylhomocysteine nucleosidase (pfs) enzyme catalyzes the direct conversion of aminodeoxyfutalosine (AFL) into dehypoxanthine futalosine (DHFL) and adenine via the hydrolysis of the N-glycosidic bond that represents an essential step in the menaquinone biosynthesis pathway (Li et al, 2011). This enzyme is an attractive drug target as it is involved in many pathways, such as ubiquinone and other terpenoid-quinone biosynthesis, cysteine and methionine metabolism, and biosynthesis of amino acids.…”

Transition States and Transition State Analogue Interactions with Enzymes

“…37,38 MTANs from E. coli and Vibrio cholera are closely related in catalytic properties and catalytic site structure. Yet, transition state analogues bind several orders of magnitude more tightly to the enzyme from E. coli .…”