Multiple isoelectric forms of bacterial penicillin-binding proteins: artefacts or genuine cellular components?

Some bacterial penicillin-binding proteins (PBPs) are reported to exist as multiple isoelectric forms. Other PBPs were examined by two-dimensional electrophoresis to establish whether multiple isoelectric forms are widespread amongst PBPs. Bacillus subtilis PBPs 3 and 5 and Escherichia coli PBPs 1b alpha and 1b gamma focussed as discrete spots with no evidence of multiple isoforms. However, E. coli PBPs 1b beta and 4 displayed isoelectric variants. The results are discussed in relation to current models of bacterial peptidoglycan structure.