Binding studies of vancomycin to the cytoplasmic peptidoglycan precursors by affinity capillary electrophoresis

The ability of vancomycin to bind three cytoplasmic peptidoglycan precursors in bacterial species was studied using affinity capillary electrophoresis (ACE). The ACE binding assay was established with the normal precursor, UDP-N-acetylmuramyl-L-Ala-D-Glu-L-Lys-D-Ala-D-Ala, from Staphylococcus aureus 209P under conditions where vancomycin served as substrate ligand included in the buffer system. This precursor was found to bind to vancomycin with a binding constant of 1.6 x 10(-5) M-1 (or a dissociation constant of 62.5 microM) obtained from Scatchard plots. No migration shifting was observed under the same conditions for the other two precursors from Leuconostoc mesenteroides VR1 and Lactobacillus casei 7469, suggesting structural modifications at the stem peptide terminus. The reduction of their affinity to vancomycin is consistent with proposed structures, UDP-N-acetylmuramyl-L-Ala-D-Glu-L-Lys-(L-Ala)-D-Ala-D-lactate and UDP-N-acetylmuramyl-L-Ala-D-Glu-L-Lys-D-Ala-D-lactate, from L. mesenteroides VR1 and L. casei 7469, respectively, based on mass spectrometry. This rapid technique provides additional evidence in the understanding of one mechanism of bacterial resistance.