MEMBRANE-BOUND LYTIC ENDOTRANSGLYCOSYLASE IN ESCHERICHIA-COLI

The gene for a novel endotype membrane-bound lytic transglycosylase, e mtA, was mapped at 26.7 min of the E. coli chromosome. EmtA is a lipop rotein with an apparent molecular mass of 22 kDa. Overexpression of th e emtA gene did not result in bacteriolysis in vivo, but the enzyme wa s shown to hydrolyze glycan strands isolated from murein by amidase tr eatment. The formation of tetra- and hexasaccharides, but no disacchar ides, reflects the endospecificity of the enzyme. The products are cha racterized by the presence of 1,6-anhydromuramic acid, indicating a ly tic transglycosylase reaction mechanism, EmtA may function as a format ting enzyme that trims the nascent murein strands produced by the mure in synthesis machinery into proper sizes, or it may be involved in the formation of tightly controlled minor holes in the murein sacculus to facilitate the export of bulky compounds across the murein barrier.