Lipid II: total synthesis of the bacterial cell wall precursor and utilization as a substrate for glycosyltransfer and transpeptidation by penicillin binding protein (PBP) 1b of Escherichia coli.

An essential feature in the life cycle of both gram positive and gram negative bacteria is the production of new cell wall. Also known as murein, the cell wall is a two-dimensional polymer, consisting of a linear, repeating N-acetylmuramic acid (MurNAc) and N-acetylglucosamine (GlcNAc) motif, cross-linked via peptides appended to MurNAc. The final steps in the maturation of murein are catalyzed by a single, bifunctional enzyme, known as a high MW, class A penicillin binding protein (PBP). PBPs catalyze polymerization of the sugar units (glycosyltransfer), as well as peptide cross-linking (transpeptidation) utilizing Lipid II as substrate. Detailed enzymology on this enzyme has been limited, due to difficulties in obtaining sufficient amounts of Lipid II, as well as the availability of a convenient and informative assay. We report the total chemical synthesis of Lipid II, as well as the development of an appropriate assay system and the observation of both catalytic transformations.