The bgl sensory system:: a transmembrane signaling pathway controlling transcriptional antitermination

The bgl system represents a family of sensory systems composed of membrane-bound sugar-sensors and transcriptional antiterminators, which regulate expression of genes involved in sugar utilization in response to the presence of the corresponding sugar in the growth medium. The BgIF sensor catalyzes different activities depending on its stimulation state: in its non-stimulated state, it phosphorylates the BgIG transcriptional regulator, thus inactivating it; in the presence of the stimulating sugar, it transports the sugar and phosphorylates it and also activates BgIG by dephosphorylation, leading to bgl operon expression. The sugar stimulates BgIF by inducing a change in its membrane topology. BgIG exists in several conformations: a dinner, which is active, and compact and non-compact monomers, which are inactive. BgIF modulates the transition of BgIG from one conformation to another, depending on sugar availability. The two Bgl proteins form a pre-complex at the membrane that dissociates upon stimulation, enabling BgIG to exert its effect on transcription.