This moiety is now incorporated in the normal
peptidoglycan synthesis and is no longer susceptible to
glycopeptide inhibition. On cross-linking during transpeptidation,
the terminal lactate is removed, often by
the non-essential gene product VanY [4] (Figure 2). An
additional non-essential gene (vanZ) has no known function.
The vanA operon is inducible, which is also rare for a
transferable resistance mechanism, by a two-component
induction system. VanS is a transmembrane protein that
autophosphorylates when it detects an incoming glycopeptide,
which then phosphylates VanR that acts on the
essential promoter of the operon. The vanA operon is
effective against all glycopeptides that can initiate induction
including teicoplanin. There are several similar
operons in VRE; the second in importance is the vanB
operon in Tn1547, which confers lower resistance to
vancomycin and none to teicoplanin because this glycopeptide
does not act as an inducer [5]. The vanC and vanE
operons employ serine instead of lactate as the glycopeptide-insusceptible
terminal moiety in the pentapeptide in
peptidoglycan synthesis [4,6].