The glucitol (sorbitol) operon express a phosphoenolpyruvate:sugar phosphotransferase system that is responsible for the uptake and catabolism of D-glucitol from the environment.
The operon is known to consist of seven genes, gut(srl)AEBDMRQ. The EIIGut complex is formed by GutA (EIIC1 domain), GutE (EIIBC2 domains), and GutB (EIIA domain) and transports D-glucitol across the inner membrane and into the cell as D-glucitol 6-phosphate. D-Glucitol 6-phosphate is then further metabolized by GutD, an NADH-dependent dehydrogenase, to the glycolytic intermediate D-fructose 6-phosphate. Expression of the gut operon is tightly controlled by a complex multicomponent regulatory system, consisting of a transcriptional repressor (GutR) and a transcriptional activator (GutM). However, the function of GutQ remains unknown.

********VARIANT CODES:*************

1.0 – position one shows the presence of sorbitol (glucitol) operon ( as in Streptococcus mutans UA159);

0.1 - position two shows the presence of the L-sorbose utilization operon (as in Escherichia coli E2348/69);

1.1 - both operons- D-Sorbitol(D-Glucitol) and L-Sorbose Utilization – are present ( as in Escherichia coli 042)
"x" - in any position stands for a missing gene in the module.

Close biochemical relationships are inherent to the L-sorbose and D-sorbitol metabolic pathways in Gram-negative bacteria. They share a common enzymic step catalysed by a D-sorbitol-6-phosphate dehydrogenase that converts D-sorbitol 6-phosphate to D-fructose 6-phosphate with the concomitant reduction of NAD+ to NADH.

It’s shown that the gene encoding the sorbose-specific L-sorbose-1-phosphate reductase could complement the lack of the sorbitol-specific D-sorbitol-6-phosphate dehydrogenase in E. coli.


*********NOTES:**************

1.In two Shigella flexneri - GutA (PTS system, glucitol/sorbitol-specific IIC component) is absent.

2. Among all Yersinias sorbitol operon is present ONLY in Yersinia enterocolitica 8081, in all others it's not found.

3. The same story with Streptococcus - only Streptococcus mutans UA159 has D-Glucitol(sorbitol) Utilization operon.

*******REFERENCES***************

1. Meredith TC, Woodard RW. Identification of GutQ from Escherichia coli as a D-arabinose 5-phosphate isomerase. J Bacteriol. 2005 Oct;187(20):6936-42. PMID: 16199563

2. Boyd, D. A., T. Thevenot, M. Gumbmann, A. L. Honeyman, and I. R. Hamilton. 2000. Identification of the operon for the sorbitol (glucitol) phosphoenolpyruvate:sugar phosphotransferase system in Streptococcus mutans. Infect. Immun. 68:925-930.

3. Brunker P, Altenbuchner J, Mattes R. Structure and function of the genes involved in mannitol, arabitol and glucitol utilization from Pseudomonas fluorescens DSM50106. Gene. 1998 Jan 5;206(1):117-26. PMID: 9461423.

4. Yebra, M. J., Perez-Martinez, G. (2002). Cross-talk between the L-sorbose and D-sorbitol (D-glucitol) metabolic pathways in Lactobacillus casei. Microbiology 148: 2351-2359. PMID: 12177329.

5. Yebra, M. J., Veyrat, A., Santos, M. A. & Pérez-Martínez, G. (2000). Genetics of L-sorbose transport and metabolism in Lactobacillus casei. J Bacteriol 182, 155-163. PMID: 10613875