Penicillin-binding proteins. Wall peptidoglycan assembly and resistance to penicillin: facts, doubts and hopes.

The assembly of the bacterial cell wall peptidoglycan relies upon the availability of a ready-made precursor, the lipid II intermediate. This intermediate is taken up by a multifunctional factory that provides the required enzymatic activities for polymer assembly at the exterior of the plasma membrane. Morphogenetic networks regulate the synthesis in a cell-cycle-dependent fashion. As essential components of the cell machinery are targets of beta-lactam antibiotics, safety devices protect the cells against these toxic agents. Controversy and consensus formation lie at the heart of the scientific research. This review focuses on questions that bacterial cell wall biochemists still strive, with increasing success, to answer.