Essential maltosyltransferase that uses maltose 1-phosphate (M1P) as the sugar donor to elongate linear or branched alpha-(1->4)-glucans. Maltooligosaccharides with a degree of polymerization (DP) superior or equal to 4 are efficient acceptors, with DP5 being optimal in the GlgE-catalyzed polymerization with M1P. Is specific for the alpha-anomer of M1P as substrate, since the beta-anomer of M1P gives no activity. Exhibits an alpha-retaining catalytic mechanism. Is also able to catalyze the reverse reaction in vitro, releasing M1P from glycogen in the presence of inorganic phosphate. Also catalyzes disproportionation reactions through maltosyl transfer between maltooligosaccharides. Is involved in a branched alpha-glucan biosynthetic pathway from trehalose, together with TreS, Mak and GlgB. [(1->4)-alpha-D-glucosyl](n) + alpha-maltose 1-phosphate = [(1->4)-alpha-D-glucosyl](n+2) + phosphate Optimum pH is 7.0 with maltohexaose as acceptor substrate. Optimum temperature is 37 degrees Celsius with maltohexaose as acceptor substrate. Glycan biosynthesis; glycogen biosynthesis. Homodimer. GlgE inactivation causes rapid death of M.tuberculosis in vitro and in mice through a self-poisoning accumulation of maltose 1-phosphate, driven by a self-amplifying feedback stress response. The unique combination of maltose 1-phosphate toxicity and gene essentiality within a synthetic lethal pathway validates GlgE as a distinct potential drug target that exploits new synergistic mechanisms to induce death in M.tuberculosis. Belongs to the glycosyl hydrolase 13 family. GlgE subfamily.