VanX is a Zn(II)-containing metalloenzyme that cleaves D-alanyl-D-alanine dipeptide (D-ala-D-ala), increasing the cytoplasmic pool of free D-ala available for use by VanA to form D-ala-D-lac. The enzyme is stereospecific and is found in solution as a mixture of monomers and dimers. The dipeptidase is a critical component of a system that mediates transposon-based, high-level vancomycin resistance in enterococci. Vancomycin acts by binding to the terminal D-ala-D-ala moiety of the bacterial peptidoglycan precursor, interfering with growth of the peptidoglycan chain and normal cell wall formation. The substitution of D-ala-D-ala by D-ala-D-lac at the extracellular terminus of the peptidoglycan chain diminishes the affinity of vancomycin by 1000-fold.
Defined by 5 residues: ARG:A-71HIS:A-116ASP:A-123GLU:A-181HIS:A-184