Structural and functional adaptation of vancomycin resistance VanT serine racemases

Journal Article · Tue Aug 11 00:00:00 EDT 2015 · mBio (Online)

DOI:https://doi.org/10.1128/mBio.00806-15· OSTI ID:1212205

Meziane-Cherif, Djalal ^[1]; Stogios, Peter J. ^[2]; Evdokimova, Elena ^[2]; Egorova, Olga ^[2]; Savchenko, Alexei ^[2]; Courvalin, Patrice ^[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)

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 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 VanT_G against L-Ser versus L-Ala implied that this enzyme relies on its membrane-bound domain for L-Ser transport 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.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: National Institutes of Health (NIH)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1212205
• Journal Information: mBio (Online), Vol. 6, Issue 4; ISSN 2150-7511
• Publisher: American Society for Microbiology
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

59 BASIC BIOLOGICAL SCIENCES