Modifications of the acyl-d-alanyl-d-alanine terminus affecting complex-formation with vancomycin

Abstract

Vancomycin forms complexes with peptides terminating in d-alanyl-d-alanine that are analogous to the biosynthetic precursors of bacterial mucopeptides. The specificity of complex-formation has been studied by means of many synthetic peptides, prepared by both solid-phase and conventional methods. The following conclusions can be drawn: (a) three amide linkages are required to form a stable complex; (b) the terminal carboxyl group must be free; (c) the carboxyl terminal and subterminal residues must be either glycine or of the d-configuration; (d) the size of the side chain in these residues greatly influences the affinity for vancomycin, a methyl group being the optimum in each case; (e) the nature of the side chain in the third and fourth residues has a smaller effect on complex-formation, but an l-configuration was somewhat better than a d-configuration in the third position. In addition to acyl-d-alanyl-d-alanine, other peptides that occur in bacterial cell walls will combine with vancomycin, although less strongly, e.g. acyl-d-alanyl-d-alpha-amino acid (where the terminal d-residue may form the cross-link in mucopeptide structure) and acyl-l-alanyl-d-glutamylglycine (a sequence found in the mucopeptide of Micrococcus lysodeikticus and related organisms). These results throw some light on the specificity of the uptake of vancomycin by living bacteria.

Determination of Noncovalent Binding Using a Continuous Stirred Tank Reactor as a Flow Injection Device Coupled to Electrospray Ionization Mass Spectrometry

“…K d values determined using the equimolar binding model developed by Gabelica et al [36], and combined with the CSTR dilution model, are presented in Table1.The results obtained for Ac-L-Lys(Ac)-D-Ala-D-Ala are similar to those reported in prior literature [1,6,7,13], where a variety of different analytical methods were used. However, the reported literature values do vary quite a bit, and this is most certainly due to slight differences in solution conditions and associated methodological accuracies.…”

“…The developed method further allowed the determination of noncovalent binding for the Ac-Lys(Ac)-Ala-Ala-OH peptide stereoisomers that have been previously described as having no binding [7]. This could be explained by the fact that the developed method is more sensitive compared with the UV spectroscopy method used by Nieto and Perkins [7]; additionally, the IT-TOF mass spectrometer used in this work may be more sensitive than mass spectrometers used in previous studies.…”

“…This could be explained by the fact that the developed method is more sensitive compared with the UV spectroscopy method used by Nieto and Perkins [7]; additionally, the IT-TOF mass spectrometer used in this work may be more sensitive than mass spectrometers used in previous studies. In this work, dissociation constants were determined in both the positive and negative ionization modes.…”

“…This peptide was chosen since its binding with vancomycin has been well studied and described in previous literature [1,3,[5][6][7].…”

“…This antibiotic binds stereospecifically to the carboxy-terminal D-Alanine-D-Alanine sequence of peptidoglycan precursors and inhibits new enzymatic crosslinking at this terminal sequence [1][2][3][4]. Numerous studies about noncovalent binding determination between vancomycin and different cell wall model targets have been performed [1,3,[5][6][7]. In an effort to build from the knowledge gained, this model has also been used to facilitate the discovery of new antibiotic leads that might exhibit their activity through the same mechanism [8,9].…”