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Title: Structural and functional adaptation of vancomycin resistance VanT serine racemases

Vancomycin resistance in Gram-positive bacteria results from the replacement of the D-alanyl–D-alanine target of peptidoglycan precursors with D-alanyl–D-lactate or D-alanyl–D-serine (D-Ala-D-Ser), to which vancomycin has low binding affinity. VanT is one of the proteins required for the production of D-Ala-D-Ser-terminating precursors by converting L-Ser to D-Ser. VanT is composed of two domains, an N-terminal membrane-bound domain, likely involved in L-Ser uptake, and a C-terminal cytoplasmic catalytic domain which is related to bacterial alanine racemases. To gain insight into the molecular function of VanT, the crystal structure of the catalytic domain of VanT G from VanG-type resistant Enterococcus faecalis BM4518 was determined. The structure showed significant similarity to type III pyridoxal 5'-phosphate (PLP)-dependent alanine racemases, which are essential for peptidoglycan synthesis. Comparative structural analysis between VanT G and alanine racemases as well as site-directed mutagenesis identified three specific active site positions centered around Asn 696 which are responsible for theL-amino acid specificity. This analysis also suggested that VanT racemases evolved from regular alanine racemases by acquiring additional selectivity toward serine while preserving that for alanine. The 4-fold-lower relative catalytic efficiency of VanT G against L-Ser versus L-Ala implied that this enzyme relies on its membrane-bound domain for L-Ser transportmore » to increase the overall rate of D-Ser production. These findings illustrate how vancomycin pressure selected for molecular adaptation of a housekeeping enzyme to a bifunctional enzyme to allow for peptidoglycan remodeling, a strategy increasingly observed in antibiotic-resistant bacteria.« less
 [1] ;  [2] ;  [2] ;  [2] ;  [2] ;  [1]
  1. Unite des Agents Antibacteriens, Paris (France)
  2. Univ. of Toronto, Toronto, ON (Canada); Center for Structural Genomics of Infectious Diseases (CSGID), New York, NY (United States)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
mBio (Online)
Additional Journal Information:
Journal Name: mBio (Online); Journal Volume: 6; Journal Issue: 4; Journal ID: ISSN 2150-7511
American Society for Microbiology
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
National Institutes of Health (NIH)
Country of Publication:
United States
OSTI Identifier: