Abstract
The nan cluster of Vibrio vulnificus, a food-borne pathogen, consists of two divergently transcribed operons, nanT(PSL)AR and nanEK nagA, required for transport and catabolism of N-acetylneuraminic acid (Neu5Ac). A mutation of nanR abolished the extensive lag phase observed for the bacteria growing on Neu5Ac and increased transcription of nanT(P) and nanE, suggesting that NanR is a transcriptional repressor of both nan operons. Intracellular accumulation of Neu5Ac was dependent on the carbon source, implying that the nan operons are also subject to catabolite repression. Hence, cAMP receptor protein (CRP) appeared to activate and repress transcription of nanT(PSL)AR and nanEK nagA, respectively. Direct bindings of NanR and CRP to the nanT(P)-nanE intergenic DNA were demonstrated by EMSA. Two adjacent NanR-binding sites centered at +44.5 and -10 and a CRP-binding site centered at -60.5 from the transcription start site of nanT(P) were identified by DNase I protection assays. Mutagenesis approaches, in vitro transcription, and isothermal titration calorimetry experiments demonstrated that N-acetylmannosamine 6-phosphate specifically binds to NanR and functions as the inducer of the nan operons. The combined results propose a model in which NanR, CRP, and N-acetylmannosamine 6-phosphate cooperate for precise adjustment of the expression level of the V. vulnificus nan cluster.
Highlights
Catabolic utilization of sialic acid is essential for the pathogenesis of enteropathogens
Two adjacent NanR-binding sites centered at ؉44.5 and ؊10 and a cAMP receptor protein (CRP)-binding site centered at ؊60.5 from the transcription start site of nanTP were identified by DNase I protection assays
The postulated V. vulnificus nan cluster consists of the genes encoding a putative transcription regulator NanR, Neu5Ac transporters NanTPSL, and proteins involved in catabolic degradation of Neu5Ac such as N-acetylneuraminate lyase (NanA), NanE, NanK, and NagA (Fig. 1B)
Summary
Catabolic utilization of sialic acid is essential for the pathogenesis of enteropathogens. Results: NanR, CRP, and ManNAc-6P regulate the V. vulnificus nan cluster required for catabolism of Neu5Ac, a sialic acid. The nan cluster of Vibrio vulnificus, a food-borne pathogen, consists of two divergently transcribed operons, nanTPSLAR and nanEK nagA, required for transport and catabolism of N-acetylneuraminic acid (Neu5Ac). The combined results propose a model in which NanR, CRP, and N-acetylmannosamine 6-phosphate cooperate for precise adjustment of the expression level of the V. vulnificus nan cluster. These adverse environments is often crucial for bacteria to survive and multiply in the intestine [1, 2]. The most abundant sialic acid is N-acetylneuraminic acid (Neu5Ac), and many intestinal commensal and pathogenic bacteria have evolved elaborate systems for the catabolic utilization of Neu5Ac. The bacteria employ different transporters to obtain Neu5Ac from the environments. ManNAc is converted into an intermediate of the central metabolism (fructose 6-phosphate) via the activities of various proteins, including NanK (N-acetylmannosamine kinase), NanE (N-acetylmannosamine-6-phosphate epimerase), and NagA (N-acetylglucosamine-6-phosphate deacetylase) as presented in Fig. 1A [8, 11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
