Differences between inner membrane and peptidoglycan-associated PBP1B dimers of Escherichia coli

Earlier studies revealed that PBP1B of Escherichia coli occurred as a monomeric as well as a dimeric form (C.A.L. Zijderveld, M.E.G. Aarsman, T. den Blaauwen, and N. Nanninga, J. Bacteriol. 173:5740-5746, 1991). In this study, the dimer of PBP1B was further analyzed. It appeared that the dimeric form could be divided into two classes. One class, which cofractionated with the cell wall fraction, could be artificially cross-linked to peptidoglycan, indicating a close association with the latter. This class of PBP1B dimers was sensitive to beta-mercaptoethanol. The second class, like the monomeric form of PBP1B, could be isolated with the inner membrane fraction. This dimeric form dissociated in the presence of zinc in combination with beta-mercaptoethanol.