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Structure and dynamics of CTX-M enzymes reveal insights into substrate accommodation by extended-spectrum

Julien Delmas1, Yu Chen, Fabio Prati

  • 1Laboratoire de Bactériologie, CHU Clermont-Ferrand, Clermont-Ferrand F-63003, France.

Journal of Molecular Biology
|November 15, 2007
PubMed

Insights

Extended-spectrum beta-lactamases (CTX-Ms) can hydrolyze oxyimino-cephalosporin antibiotics like ceftazidime. A specific mutation (Asp240Gly) in CTX-M-16 enhances this activity by altering enzyme structure and ceftazidime binding.

Area of Science:

  • Biochemistry
  • Structural Biology
  • Microbiology

Background:

  • Oxyimino-cephalosporins, including ceftazidime, are crucial antibiotics against bacterial infections.
  • Widespread antibiotic use has led to the emergence of highly prevalent extended-spectrum beta-lactamases (CTX-Ms).
  • Certain CTX-M variants, like Asp240Gly mutants, exhibit enhanced hydrolysis of ceftazidime, posing a therapeutic challenge.

Purpose of the Study:

  • To elucidate the structural and dynamic mechanisms by which the Asp240Gly substitution in CTX-M-16 confers enhanced ceftazidime hydrolysis.
  • To understand the molecular basis of antibiotic resistance in CTX-M enzymes.

Main Methods:

  • Crystallographic structure determination of CTX-M-16 (Asp240Gly mutant) complexed with a ceftazidime-like glycylboronic acid at 1.80 Å resolution.
  • Molecular dynamics simulations of the acyl-enzyme complex to analyze enzyme dynamics.

Main Results:

  • The Asp240Gly substitution facilitates the accommodation of ceftazidime within the CTX-M-16 active site.
  • This mutation leads to the deep insertion of ceftazidime's C7 side chain into the catalytic pocket.
  • Orchestrated movements of active site residues (Ser70, beta 3 strand, omega loop) and key interactions (residues 237, 235) are observed, favoring hydrolysis.

Conclusions:

  • The Asp240Gly mutation in CTX-M-16 significantly alters enzyme dynamics and active site conformation.
  • These structural changes promote enhanced binding and hydrolysis of ceftazidime, contributing to antibiotic resistance.
  • Understanding these mechanisms is vital for developing novel antibiotics or resistance inhibitors.

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