Crystal Structure of Vanx - The Source of Vancomycin Resistance.
C. Park, D. Bussiere, S. Muchmore, J. Severin, K. Walter, T. Holzman,
S. Pratt, L. Katz, J. Greer
Abbott Laboratories, 100
Abbott Park Rd., Abbott Park, IL 60064
To keep the lead in the race with microbes that are developing resistance to vancomycin with threatening speed, researchers have found suitable target genes like vanR, vanS, vanH, vanA and vanX. The vanX gene of gram-positive bacteria is required for production of a dipeptidase (VanX) which hydrolyses D-Ala-D-Ala, thereby obstructing synthesis of D-Ala-D-Ala containing pentapeptide and subsequent binding of vancomycin to the bacterial cell surface. X-ray crystallographic studies of VanX have been carried out with the purpose of clarifying the mechanism of hydrolysis and designing drug candidates capable of inhibiting the VanX function and supressing the clinical vancomycin resistance. VanX is a Zn-dependent D,D-dipeptidase with 202 residues, M.W. of 23,365. Crystals of vanX were obtained in Space Group P2(1) with cell dimensions of a=83.32, b=45.26, c=171.33 A, beta=104.02. From the Patterson rotation function search, it was expected that six VanX molecules are in one asymmetric unit related by non-crystallographic symmetry axes. The structure has been solved by the Multiple Isomorphous Replacement (MIR) method with several heavy atom derivatives at 2.7 A. The five local 2-folds are generating a column of six VanX proteins along the c-axis. The Zn atom and all the liganding side chains are identified in the active site located on top of four anti-parallel beta strands and bordered by a helix and a loop. The refined VanX structure will be used to aid in designing inhibitors of VanX for coadministration with vancomycin to overcome resistance.