Binding of a dimeric derivative of vancomycin to l-Lys-d-Ala- d-lactate in solution and at a surface Original Research Article

Background The emergence of bacteria that are resistant to vancomycin (V), a glycopeptide antibiotic, results from the replacement of the carboxy-terminal d-Ala-d-Ala of bacterial cell wall precursors by d-Ala-d-lactate. Recently, it has been demonstrated that covalent dimeric variants of V are active against vancomycin-resistant enterococci (VRE). To study the contribution of divalency to the activities of these variants, we modeled the interactions of V and a dimeric V with l-Lys-d-Ala-d-lactate, an analog of the cell-wall precursors of the vancomycin-resistant bacteria. Results A dimeric derivative of V (V-Rd-V) was found to be much more effective than V in inhibiting the growth of VRE. The interactions of V and V-Rd-V with a monomeric lactate ligand — diacetyl-l-Lys-d-Ala-d-lactate (AccKdAdLac) — and a dimeric derivative of l-Lys-d-Ala-d-lactate (Lac-R′d-Lac) in solution have been examined using isothermal titration calorimetry and UV spectroscopy titrations; the results reveal that V-Rd-V binds Lac-R′d-Lac approximately 40 times more tightly than V binds Ac2KdAdLac. Binding of V and of V-Rd-V to Nα-Ac-l-Lys-d-Ala-d-lactate presented on the surface of mixed self-assembled monolayers (SAMs) of alkanethiolates on gold indicates that the apparent off-rate for dissociation of V-Rd-V from the surface is much slower than that of V from the same surface. Conclusions