Three essential genes
(vanH, vanA and vanX) are responsible for initiating an
alternative route to peptidoglycan synthesis that removes
the glycopeptide binding site of the D-alanyl-D-alanine
group on the pentapeptide. This alternative route involves
reversing the formation of the D-alanyl-D-alanine
moiety (VanX) to release free D-alanine, hydrogenating
pyruvate to form lactate (VanH), which is then ligated
with the freed D-alanine to provide D-alanyl-lactate