Glycopeptide antibiotic activity and the possible role of dimerization: A model for biological signaling

It is demonstrated that the presence of bacterial cell wall analogues may either enhance or, in the case of ristocetin A, oppose dimerization of glycopeptide antibiotics. These observations may imply that dimerization plays a role in the mode of action of these antibiotics, and a mechanism is proposed to take account of this possibility. The glycopeptide dimers are also found to be formed more exothermically in the presence of cell wall analogues, and the nature of biological signaling events is discussed in this context. It is pointed out that binding enthalpy (rather than simply binding free energy, ΔG) may be an important quantity in signaling events. If this is so, then oligomers may be abundant in signaling processes partly because the extended aggregates they form are able to cooperatively amplify the conformational changes which are incurred on ligand binding, which occur through relatively small changes in free energy but larger opposing changes in enthalpy and entropy.