Cell division in staphylococci: a clue to the three-dimensional structure of peptidoglycan

The composition of the monomeric unit of staphylococcal peptidoglycan has been known since the late 1960s. However, the three-dimensional structure of this macromolecule has been unclear. Staphylococci divide with expansion of a central cross wall into a peripheral hemisphere under conditions that suggest that additional monomers are not introduced, but rather that the shape of existing monomers is changed. The monomeric unit can be divided into a glycan chain piece, a connecting peptide, and a peptide chain piece, which define a solid parallelogram. In the proposed model, appropriate change in the angle of the glycan chain with respect to the peptide chain doubles the surface, as required to deform cross wall into peripheral wall. Furthermore, cross wall peptidoglycan is synthesized in a spiral, which becomes deformed into a spiral to form peripheral wall, and the glycan chain is twisted with two disaccharide units per turn. Insights from the model can be applied to other peptidoglycans and can help explain the mechanism for start of cell division, the functions of various penicillin-binding proteins, the method of resistance to methicillin, and the occurrence of osmotically growth-dependent bacteria.