glpFKD

glpFKD refers to a glycerol utilization module found in many bacteria, especially in members of the Enterobacterales. It comprises three genes: glpF, glpK, and glpD. GlpF encodes a glycerol uptake facilitator, a membrane channel that increases glycerol import. GlpK encodes glycerol kinase, which phosphorylates glycerol to glycerol-3-phosphate. GlpD encodes glycerol-3-phosphate dehydrogenase, which oxidizes glycerol-3-phosphate to dihydroxyacetone phosphate (DHAP), an intermediate that enters glycolysis.

In normal physiology, the operon enables efficient utilization of glycerol as a carbon and energy source. Glycerol is taken up via GlpF, phosphorylated by GlpK to glycerol-3-phosphate, and then converted by GlpD to DHAP, feeding the glycolytic pathway and energy production. The activity of glpFKD is tightly regulated to coordinate glycerol metabolism with the cell’s carbon status.

Regulation typically involves the GlpR repressor, which binds to the glpFKD promoter and represses transcription in the absence of glycerol-3-phosphate. When glycerol-3-phosphate accumulates, GlpR repression is alleviated, permitting transcription. In many species, cAMP receptor protein (CRP) and the cellular cAMP level further modulate expression, particularly under carbon-limited conditions, providing positive regulation in concert with GlpR control.

Distribution and relevance vary by species; glpFKD is a common model system for studying bacterial carbohydrate uptake, regulation, and metabolic flux. It is also used in basic research and metabolic engineering to explore glycerol utilization pathways.