In Helicobacter pylori, LuxS is a key enzyme in cysteine provision through a reverse transsulfuration pathway.
In many bacteria, LuxS functions as a quorum-sensing molecule synthase. However, it also has a second, more central metabolic function in the activated methyl cycle (AMC), which generates the S-adenosylmethionine required by methyltransferases and recycles the product via methionine. Helicobacter pylori lacks an enzyme catalyzing homocysteine-to-methionine conversion, rendering the AMC incomplete and thus making any metabolic role of H. pylori LuxS (LuxS(Hp)) unclear. Interestingly, luxS(Hp) is located next to genes annotated as cysK(Hp) and metB(Hp), involved in other bacteria in cysteine and methionine metabolism. We showed that isogenic strains carrying mutations in luxS(Hp), cysK(Hp), and metB(Hp) could not grow without added cysteine (whereas the wild type could), suggesting roles in cysteine synthesis. Growth of the DeltaluxS(Hp) mutant was restored by homocysteine or cystathionine and growth of the DeltacysK(Hp) mutant by cystathionine only. The DeltametB(Hp) mutant had an absolute requirement for cysteine. Metabolite analyses showed that S-ribosylhomocysteine accumulated in the DeltaluxS(Hp) mutant, homocysteine in the DeltacysK(Hp) mutant, and cystathionine in the DeltametB(Hp) mutant. This suggests that S-ribosylhomocysteine is converted by LuxS(Hp) to homocysteine (as in the classic AMC) and thence by CysK(Hp) to cystathionine and by MetB(Hp) to cysteine. In silico analysis suggested that cysK-metB-luxS were acquired by H. pylori from a Gram-positive source. We conclude that cysK-metB-luxS encode the capacity to generate cysteine from products of the incomplete AMC of H. pylori in a process of reverse transsulfuration. We recommend that the misnamed genes cysK(Hp) and metB(Hp) be renamed mccA (methionine-to-cysteine-conversion gene A) and mccB, respectively.
Doherty
Neil C
NC
Centre for Biomolecular Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom. msxfs@exmail.nottingham.ac.uk
Shen
Feifei
F
Halliday
Nigel M
NM
Barrett
David A
DA
Hardie
Kim R
KR
Winzer
Klaus
K
Atherton
John C
JC
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D013437:Carbon-Sulfur Lyases / Q000235:genetics / Q000378:metabolism*; D019295:Computational Biology; D003470:Culture Media / Q000737:chemistry; D003540:Cystathionine / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D055786:Gene Knockout Techniques; D023061:Gene Order; D022761:Gene Transfer, Horizontal; D006094:Gram-Positive Bacteria / Q000235:genetics; D016480:Helicobacter pylori / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D006710:Homocysteine / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D017422:Sequence Analysis, DNA; D013455:Sulfur / Q000378:metabolism*
D001426:Bacterial Proteins; D003470:Culture Media; D004269:DNA, Bacterial; D006710:Homocysteine; D003540:Cystathionine; D013455:Sulfur; D013437:Carbon-Sulfur Lyases; C117753:LuxS protein, Bacteria; D003545:Cysteine