Related Experiment Videos
A putative pathway for perosamine biosynthesis is the first function encoded within the rfb region of Vibrio cholerae
U H Stroeher1, L E Karageorgos, M H Brown
1Department of Microbiology and Immunology, University of Adelaide, Australia.
Insights
The Vibrio cholerae O1 rfb genes encode enzymes for perosamine biosynthesis, crucial for O-antigen lipopolysaccharide structure. These genes are highly conserved, indicating evolutionary stability in Vibrio cholerae.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- The O-antigen of Vibrio cholerae O1 lipopolysaccharide is a key virulence factor.
- Perosamine is a critical component of the O-antigen backbone structure.
Purpose of the Study:
- To elucidate the genetic basis of perosamine biosynthesis in Vibrio cholerae O1.
- To characterize the enzymes and pathway involved in perosamine synthesis.
Main Methods:
- Bioinformatic analysis of the rfb gene cluster (rfbA,B,D,E).
- Homology-based prediction of enzyme functions.
- Comparative sequence analysis of Vibrio cholerae isolates.
Main Results:
- The rfbA,B,D,E genes encode enzymes for perosamine synthesis from fructose 6-phosphate.
- Predicted enzymes include phosphomannose isomerase-guanosine diphosphomannose pyrophosphorylase, phosphomanno-mutase, oxido reductase, and perosamine synthetase.
- The nucleotide sequences of these genes are highly conserved between classical and El Tor strains.
Conclusions:
- The identified genes and predicted enzymes provide a framework for understanding perosamine biosynthesis.
- The observed sequence conservation suggests strong evolutionary pressure on these genes.
- Further studies are warranted to experimentally validate enzyme functions and the complete pathway.
Abstract:
The first four genes (rfbA,B,D,E) of the rfb region of Vibrio cholerae O1 are predicted to encode the enzymes required for the biosynthesis of perosamine, which constitutes the backbone structure of the O-antigen of the lipopolysaccharide. Based on homology to known proteins/protein families, the following functions are predicted: RfbA, phosphomannose isomerase-guanosine diphosphomannose pyrophosphorylase; RfbB, phosphomanno-mutase; RfbD, oxido reductase and RfbE, perosamine synthetase (amino-transferase). Thus, perosamine is synthesized from fructose 6-phosphate via the intermediates mannose 6-phosphate by RfbA, to mannose 1-phosphate by RfbB, to GDP-mannose by RfbA, to GDP-4-keto-6-dideoxymannose by RfbD and to GDP-perosamine by RfbE. This final product would then serve as the substrate for the addition of the tetronate, which could then be polymerized into the O-antigen for transfer to the lipid A plus core oligosaccharide and export to the cell surface. The organization of these genes are such that one would expect them to be translationally coupled as part of the rfb operon. However, the absence of readily detectable promoter sequences suggests low levels of transcription, in line with other studies. The nucleotide sequence of these genes is absolutely conserved in the two isolates 569B (classical, Inaba) and O17 (El Tor, Ogawa) which were expected to show maximal sequence variation. This suggests very tight constraints on the micro-evolution within these sequences.