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X-ray analysis of the NMC-A beta-lactamase at 1.64-A resolution, a class A carbapenemase with broad substrate
P Swarén1, L Maveyraud, X Raquet
1Groupe de Cristallographie Biologique, Institut de Pharmacologie et de Biologie Structurale, UPR 9062 CNRS, 205 route de Narbonne, F-31077 Toulouse CEDEX, France.
Abstract:
The treatment of infectious diseases by penicillin and cephalosporin antibiotics is continuously challenged by the emergence and the dissemination of the numerous TEM and SHV mutant beta-lactamases with extended substrate profiles. These class A beta-lactamases nevertheless remain inefficient against carbapenems, the most effective antibiotics against clinically relevant pathogens. A new member of this enzyme class, NMC-A, was recently reported to hydrolyze at high rates, and hence destroy, all known beta-lactam antibiotics, including carbapenems and cephamycins. The crystal structure of NMC-A was solved to 1.64-A resolution, and reveals modifications in the topology of the substrate-binding site. While preserving the geometry of the essential catalytic residues, the active site of the enzyme presents a disulfide bridge between residues 69 and 238, and certain other structural differences compared with the other beta-lactamases. These unusual features in class A beta-lactamases involve amino acids that participate in enzyme-substrate interactions, which suggested that these structural factors should be related to the very broad substrate specificity of this enzyme. The comparison of the NMC-A structure with those of other class A enzymes and enzyme-ligand complexes, indicated that the position of Asn-132 in NMC-A provides critical additional space in the region of the protein where the poorer substrates for class A beta-lactamases, such as cephamycins and carbapenems, need to be accommodated.
Insights
A novel beta-lactamase, NMC-A, efficiently destroys all beta-lactam antibiotics, including carbapenems. Its unique structure, particularly Asn-132, explains its broad substrate specificity, posing a significant challenge to infectious disease treatment.
Area of Science:
- Microbiology
- Structural Biology
- Drug Discovery
Background:
- Emergence of mutant beta-lactamases (TEM, SHV) challenges antibiotic efficacy.
- Class A beta-lactamases are typically ineffective against carbapenems.
- NMC-A is a novel class A beta-lactamase with broad-spectrum hydrolytic activity.
Purpose of the Study:
- To elucidate the structural basis for NMC-A's broad substrate specificity.
- To understand how NMC-A overcomes resistance to carbapenems and cephamycins.
Main Methods:
- X-ray crystallography of NMC-A at 1.64-A resolution.
- Comparative structural analysis with other class A beta-lactamases.
- Analysis of enzyme-ligand complexes.
Main Results:
- NMC-A crystal structure reveals modifications in the substrate-binding site topology.
- A unique disulfide bridge (residues 69 and 238) and other differences were observed.
- The position of Asn-132 provides crucial space for accommodating carbapenems and cephamycins.
Conclusions:
- NMC-A's structural adaptations, especially Asn-132, confer broad substrate specificity.
- These features explain its high hydrolysis rates for carbapenems and cephamycins.
- NMC-A represents a significant threat to current antibiotic treatments for infectious diseases.