Understanding the longevity of the β-lactam antibiotics and of antibiotic/β-lactamase inhibitor combinations (original) (raw)

Molecular evolution of ubiquitous ?-lactamases towards extended-spectrum enzymes active against newer ?-lactam antibiotics

Molecular Microbiology, 1990

Gram-negative bacteria. The two ubiquitous types of enzyme have a large spectrum of activity and preferentially hydrolyse the penicillins as well as some first-and second-generation cephalosporins. Recently, point mutations in the corresponding genes have been observed, apparently selected for, in the clinical setting, by originally '|3-lactamasestable' third-generation cephalosporins or by monobactams, vi/hich fall into the substrate range of the mutant or 'extended-spectrum' |j-lactamases. The point mutations are clustered in three areas, each adjacent to one of the seven evolutionarily conserved boxes described by Joris etal. (1988). The substituted amino acids at positions 102 (adjacent to the iv-3 helix), 162 (adjacent to the i«-7 helix) and 235,236 and 237 (on the ii-3 strand) are located in close proximity to the active-site cavity and are thought to open up novel enzyme-substrate interactions, involving, in particular, the oxyimino moieties of the newer ;3-lactam compounds.

Structural Aspects for Evolution of β-Lactamases from Penicillin-Binding Proteins

Journal of the American Chemical Society, 2003

Penicillin-binding proteins (PBPs), biosynthetic enzymes of bacterial cell wall assembly, and -lactamases, resistance enzymes to -lactam antibiotics, are related to each other from an evolutionary point of view. Massova and Mobashery (Antimicrob. Agents Chemother. 1998, 42, 1-17) have proposed that for -lactamases to have become effective at their function as antibiotic resistance enzymes, they would have had to undergo structure alterations such that they would not interact with the peptidoglycan, which is the substrate for PBPs. A cephalosporin analogue, 7 -[N-Acetyl-L-alanyl-γ-D-glutamyl-L-lysine]-3-acetoxymethyl-3-cephem-carboxylic acid (compound 6), was conceived and synthesized to test this notion. The X-ray structure of the complex of this cephalosporin bound to the active site of the deacylation-deficient Q120L/Y150E variant of the class C AmpC -lactamase from Escherichia coli was solved at 1.71 Å resolution. This complex revealed that the surface for interaction with the strand of peptidoglycan that acylates the active site, which is present in PBPs, is absent in the -lactamase active site. Furthermore, insertion of a peptide in the -lactamase active site at a location where the second strand of peptidoglycan in some PBPs binds has effectively abolished the possibility for such interaction with the -lactamase. A 2.6 ns dynamics simulation was carried out for the complex, which revealed that the peptidoglycan surrogate (i.e., the active-site-bound ligand) undergoes substantial motion and is not stabilized for binding within the active site. These factors taken together disclose the set of structure modifications in the antibiotic resistance enzyme that prevent it from interacting with the peptidoglycan, en route to achieving catalytic proficiency for their intended function.

Variations within Class-A b-Lactamase Physiochemical Properties Reflect Evolutionary and Environmental Patterns, but not Antibiotic Specificity

2013

The bacterial enzyme b-lactamase hydrolyzes the b-lactam ring of penicillin and chemically related antibiotics, rendering them ineffective. Due to rampant antibiotic overuse, the enzyme is evolving new resistance activities at an alarming rate. Related, the enzyme’s global physiochemical properties exhibit various amounts of conservation and variability across the family. To that end, we characterize the extent of property conservation within twelve different class-A b-lactamases, and conclusively establish that the systematic variations therein parallel their evolutionary history. Large and systematic differences within electrostatic potential maps and pairwise residue-to-residue couplings are observed across the protein, which robustly reflect phylogenetic outgroups. Other properties are more conserved (such as residue pKa values, electrostatic networks, and backbone flexibility), yet they also have systematic variations that parallel the phylogeny in a statistically significant w...

β-Lactamases: A Focus on Current Challenges

Cold Spring Harbor Perspectives in Medicine, 2016

b-Lactamases, the enzymes that hydrolyze b-lactam antibiotics, remain the greatest threat to the usage of these agents. In this review, the mechanism of hydrolysis is discussed for both those enzymes that use serine at the active site and those that require divalent zinc ions for hydrolysis. The b-lactamases now include .2000 unique, naturally occurring amino acid sequences. Some of the clinically most important of these are the class A penicillinases, the extended-spectrum b-lactamases (ESBLs), the AmpC cephalosporinases, and the carbapenem-hydrolyzing enzymes in both the serine and metalloenzyme groups. Because of the versatility of these enzymes to evolve as new b-lactams are used therapeutically, new approaches to antimicrobial therapy may be required.

Variations within Class-A β-Lactamase Physiochemical Properties Reflect Evolutionary and Environmental Patterns, but not Antibiotic Specificity

PLoS Computational Biology, 2013

The bacterial enzyme b-lactamase hydrolyzes the b-lactam ring of penicillin and chemically related antibiotics, rendering them ineffective. Due to rampant antibiotic overuse, the enzyme is evolving new resistance activities at an alarming rate. Related, the enzyme's global physiochemical properties exhibit various amounts of conservation and variability across the family. To that end, we characterize the extent of property conservation within twelve different class-A b-lactamases, and conclusively establish that the systematic variations therein parallel their evolutionary history. Large and systematic differences within electrostatic potential maps and pairwise residue-to-residue couplings are observed across the protein, which robustly reflect phylogenetic outgroups. Other properties are more conserved (such as residue pK a values, electrostatic networks, and backbone flexibility), yet they also have systematic variations that parallel the phylogeny in a statistically significant way. Similarly, the above properties also parallel the environmental condition of the bacteria they are from in a statistically significant way. However, it is interesting and surprising that the only one of the global properties (protein charge) parallels the functional specificity patterns; meaning antibiotic resistance activities are not significantly constraining the global physiochemical properties. Rather, extended spectrum activities can emerge from the background of nearly any set of electrostatic and dynamic properties.

Past and Present Perspectives on β-Lactamases

Antimicrobial Agents and Chemotherapy, 2018

β-Lactamases, the major resistance determinant for β-lactam antibiotics in Gram-negative bacteria, are ancient enzymes whose origins can be traced back millions of years ago. These well-studied enzymes, currently numbering almost 2,800 unique proteins, initially emerged from environmental sources, most likely to protect a producing bacterium from attack by naturally occurring β-lactams. Their ancestors were presumably penicillin-binding proteins that share sequence homology with β-lactamases possessing an active-site serine. Metallo-β-lactamases also exist, with one or two catalytically functional zinc ions. Although penicillinases in Gram-positive bacteria were reported shortly after penicillin was introduced clinically, transmissible β-lactamases that could hydrolyze recently approved cephalosporins, monobactams, and carbapenems later became important in Gram-negative pathogens. Nomenclature is based on one of two major systems. Originally, functional classifications were used, ba...

b-Lactams: chemical structure, mode of action and mechanisms of resistance

This synopsis summarizes the key chemical and bacteriological characteristics of b-lactams, penicillins, cephalosporins, carbanpenems, monobactams and others. Particular notice is given to first-generation to fifth-generation cephalosporins. This review also summarizes the main resistance mechanism to antibiotics, focusing particular attention to those conferring resistance to broad-spectrum cephalosporins by means of production of emerging cephalosporinases (extended-spectrum b-lactamases and AmpC b-lactamases), target alteration (penicillin-binding proteins from methicillin-resistant Staphylococcus aureus) and membrane transporters that pump b-lactams out of the bacterial cell.

Evolution of class C β-lactamases: factors influencing their hydrolysis and recognition mechanisms

Theoretical Chemistry Accounts, 2008

The most common bacterial resistance mechanism to β-lactam antibiotics is the production of β-lactamases. So far, β-lactamases have been classified into four different classes, three of them (A, C and D) have a serine in the active site as the nucleophilic group, which attacks to lactam antibiotic. Despite the large number of kinetic and theoretical studies and many native and complexed β-lactamases crystal structures, the mechanism by which they act is not well understood. The aim of this review is to show the different hypotheses which have been proposed to explain the hydrolysis mechanisms for class A and C lactamases and to cast light onto the interactions between the antibiotic and the Enterobacter cloacae P99 (a class C β-lactamase) in the Henry-Michaelis complex formed previous to the serine attack. Knowledge of these crucial points is essential for obtaining new β-lactam antibiotics not vulnerable to β-lactamases in order to minimize bacterial resistance.