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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 VanTG 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 VanTG and alanine racemases as well as site-directed mutagenesis identified three specific active site positions centered around Asn696 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 VanTG against L-Ser versus L-Ala implied that this enzyme relies on its membrane-bound domain for L-Ser transport to increase the overallmore » 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:
OSTI Identifier:
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 Laboratory (ANL), Argonne, IL (United States)
Sponsoring Org:
National Institutes of Health (NIH), New York, NY (United States)
Country of Publication:
United States