FIGURE 6.

Proposed regulatory role of the phosphorylated isoform of GlgE as a molecular switch in α-glucan synthesis in M. tuberculosis. Distinct from the classic glycogen pathway, the newly identified GlgE pathway comprises four successive enzymatic steps from trehalose to an α-glucan polymer that may contribute to biosynthesis of cytosolic glycogen, capsular glucan, and/or methylglucose lipopolysaccharide-related α-glucan derivatives. In response to external stimuli, the mycobacterial Ser/Thr kinase PknB is autophosphorylated. This induces GlgE phosphorylation (P) on seven Ser/Thr residues. As a result, the maltosyltransferase activity of the Ser/Thr phosphorylated GlgE is inhibited.