Oritavancin Exhibits Dual Mode of Action to Inhibit Cell-Wall Biosynthesis in Staphylococcus aureus


Journal of Molecular Biology Volume 377, Issue 1, 14 March 2008, Pages 281-293

ABSTRACT
Solid-state NMR measurements performed on intact whole cells of Staphylococcus aureus labeled selectively in vivo have established that des-N-methylleucyl oritavancin (which has antimicrobial activity) binds to the cell-wall peptidoglycan, even though removal of the terminal N-methylleucyl residue destroys the d-Ala-d-Ala binding pocket. By contrast, the des-N-methylleucyl form of vancomycin (which has no antimicrobial activity) does not bind to the cell wall. Solid-state NMR has also determined that oritavancin and vancomycin are comparable inhibitors of transglycosylation, but that oritavancin is a more potent inhibitor of transpeptidation. This combination of effects on cell-wall binding and biosynthesis is interpreted in terms of a recent proposal that oritavancin-like glycopeptides have two cell-wall binding sites: the well-known peptidoglycan d-Ala-d-Ala pentapeptide stem terminus and the pentaglycyl bridging segment. The resulting dual mode of action provides a structural framework for coordinated cell-wall assembly that accounts for the enhanced potency of oritavancin and oritavancin-like analogues against vancomycin-resistant organisms.

Chemical structures of four glycopeptides (left column) and their des-N-methylleucyl forms (right column). The terminal leucyl residue of the aglycon core of each glycopeptide is highlighted. Minimum inhibitory concentrations for the growth of vancomycin-susceptible Gram-positive bacteria (see Materials and Methods) are in red.

A comparison of inhibition of cross-linking from the 30.4-MHz 15N{13C} REDOR spectra of whole cells of S. aureus grown on media containing [15N]glycine and d-[1-13C]alanine and a racemase inhibitor (control, black), plus therapeutic doses of penicillin (blue), [19F]oritavancin (green), or vancomycin (red). Full-echo spectra normalized to the control are shown at the bottom of the figure and REDOR differences at the top. The REDOR difference measures the relative number of cross-links per peptidoglycan pentagycyl bridging segment. Vancomycin has the least effect on cross-linking and penicillin the largest effect.

Complete accounting of whole-cell d-alanine. Experimental deconvolution of the normalized 75.5-MHz carbonyl-carbon spectra of the four S. aureus samples are shown, with a structure color coding indicated in the top spectrum. Total label incorporation was 1.00 for the control and 0.53, 0.37, and 0.72 for the vancomycin, oritavancin, and penicillin-treated cells, respectively.

Space-filling model of the des-N-methylleucyl--[19F]oritavancin complex with the peptidoglycan of S. aureus (right), consistent with the results. The drug is in dark gray and the peptidoglycan components in light gray. The corresponding complex with [19F]oritavancin (left) has slightly altered positions of the d-Ala-d-Ala stem terminus and the fluorobiphenyl moiety.