FhlB

FhlB is a transcriptional activator in Escherichia coli that plays a crucial role in the metabolic regulation of formate utilization. It is a key component of the complex regulatory network that controls the expression of genes involved in one-carbon metabolism, particularly the genes encoding the enzyme formate dehydrogenase (FDH) and the formate-H2 lyase complex. FhlB is activated by binding of cyclic AMP (cAMP) and the cAMP receptor protein (Crp). This cAMP-Crp complex then interacts with FhlB, leading to its activation. Activated FhlB is a DNA-binding protein that binds to specific promoter regions of target genes, thereby enhancing their transcription. This activation is essential for the efficient assimilation of formate as a carbon and energy source, especially under anaerobic conditions. FhlB's regulation is also influenced by the availability of formate itself and by other signaling molecules within the cell. Mutations in the fhlB gene lead to a significant decrease in the expression of genes involved in formate metabolism, impairing the bacterium's ability to grow on formate. Understanding FhlB's function provides insight into how E. coli adapts its metabolic pathways to utilize diverse carbon sources.