1,2,4-Triazole-3-thione Compounds as Inhibitors of Dizinc Metallo-β-lactamases.

Metallo-β-lactamases (MBLs) cause resistance of Gram-negative bacteria to β-lactam antibiotics and are of serious concern, because they can inactivate the last-resort carbapenems and because MBL inhibitors of clinical value are still lacking. We previously identified the original binding mode of 4-amino-2,4-dihydro-5-(2-methylphenyl)-3H-1,2,4-triazole-3-thione (compound IIIA) within the dizinc active site of the L1 MBL. Herein we present the crystallographic structure of a complex of L1 with the corresponding non-amino compound IIIB (1,2-dihydro-5-(2-methylphenyl)-3H-1,2,4-triazole-3-thione).

The Inactivation of a New Peptidoglycan Hydrolase Pmp23 Leads to Abnormal Septum Formation in Streptococcus pneumoniae.

The bacterial peptidoglycan is the major component of the cell wall which integrity is essential to cell survival. In a previous work, we identified, in the positive-Gram pathogen Streptococcus pneumoniae , a unique protein containing a new putative peptidoglycan hydrolytic domain named PECACE (PEptidoglycan CArbohydrate Cleavage Enzyme). In this study, we characterise the physiological function of this protein called Pmp23 (Pneumococcal Membrane Protein of 23 kDa).

Structural basis for the broad-spectrum inhibition of metallo-beta-lactamases by thiols.

The development of broad-spectrum metallo-beta-lactamase (MBL) inhibitors is challenging due to structural diversity and differences in metal utilisation by these enzymes. Analysis of structural data, followed by non-denturing mass spectrometric analyses, identified thiols proposed to inhibit representative MBLs from all three sub-classes: B1, B2 and B3. Solution analyses led to the identification of broad spectrum inhibitors, including potent inhibitors of the CphA MBL (Aeromonas hydrophila).

Mutational analysis of the zinc- and substrate-binding sites in the CphA metallo-beta-lactamase from Aeromonas hydrophila.

The subclass B2 CphA (Carbapenemase hydrolysing Aeromonas) beta-lactamase from Aeromonas hydrophila is a Zn(2+)-containing enzyme that specifically hydrolyses carbapenems. In an effort to evaluate residues potentially involved in metal binding and/or catalysis (His(118), Asp(120), His(196) and His(263)) and in substrate specificity (Val(67), Thr(157), Lys(224) and Lys(226)), site-directed mutants of CphA were generated and characterized. Our results confirm that the first zinc ion is in interaction with Asp(120) and His(263), and thus is located in the 'cysteine' zinc-binding site.

Trapping of an acyl-enzyme intermediate in a penicillin-binding protein (PBP)-catalyzed reaction.

Class A penicillin-binding proteins (PBPs) catalyze the last two steps in the biosynthesis of peptidoglycan, a key component of the bacterial cell wall. Both reactions, glycosyl transfer (polymerization of glycan chains) and transpeptidation (cross-linking of stem peptides), are essential for peptidoglycan stability and for the cell division process, but remain poorly understood. The PBP-catalyzed transpeptidation reaction is the target of beta-lactam antibiotics, but their vast employment worldwide has prompted the appearance of highly resistant strains, thus requiring concerted efforts towards an understanding of the transpeptidation reaction with the goal of developing better antibacterials.

The three-dimensional structure of VIM-2, a Zn-beta-lactamase from Pseudomonas aeruginosa in its reduced and oxidised form.

The crystal structures of the universally widespread metallo-beta-lactamase (MBL) Verona integron-encoded MBL (VIM)-2 from Pseudomonas aeruginosa have been solved in their native form as well as in an unexpected oxidised form. This carbapenem-hydrolysing enzyme belongs to the so-called B1 subfamily of MBLs and shares the folding of alpha beta/beta alpha sandwich, consisting of a core of beta-sheet surrounded by alpha-helices. Surprisingly, it showed a high tendency to be strongly oxidised at the catalytic cysteine located in the Cys site, Cys221, which, in the oxidised structure, becomes a cysteinesulfonic residue.

Structural insights into the design of inhibitors for the L1 metallo-beta-lactamase from Stenotrophomonas maltophilia.

One mechanism by which bacteria can escape the action of beta-lactam antibiotics is the production of metallo-beta-lactamases. Inhibition of these enzymes should restore the action of these widely used antibiotics. The tetrameric enzyme L1 from Stenotrophomonas maltophilia was used as a model system to determine a series of high-resolution crystal structures of apo, mono and bi-metal substituted proteins as well as protein-inhibitor complexes.

Structure-based design of small peptide inhibitors of protein kinase CK2 subunit interaction.

X-ray crystallography studies, as well as live-cell fluorescent imaging, have recently challenged the traditional view of protein kinase CK2. Unbalanced expression of catalytic and regulatory CK2 subunits has been observed in a variety of tissues and tumours. Thus the potential intersubunit flexibility suggested by these studies raises the likely prospect that the CK2 holoenzyme complex is subject to disassembly and reassembly.

Competitive inhibitors of the CphA metallo-beta-lactamase from Aeromonas hydrophila.

Various inhibitors of metallo-beta-lactamases have been reported; however, none are effective for all subgroups. Those that have been found to inhibit the enzymes of subclass B2 (catalytically active with one zinc) either contain a thiol (and show less inhibition towards this subgroup than towards the dizinc members of B1 and B3) or are inactivators behaving as substrates for the dizinc family members. The present work reveals that certain pyridine carboxylates are competitive inhibitors of CphA, a subclass B2 enzyme.

Penicillin binding proteins: key players in bacterial cell cycle and drug resistance processes.

Bacterial cell division and daughter cell formation are complex mechanisms whose details are orchestrated by at least a dozen different proteins. Penicillin-binding proteins (PBPs), membrane-associated macromolecules which play key roles in the cell wall synthesis process, have been exploited for over 70 years as the targets of the highly successful beta-lactam antibiotics. The increasing incidence of beta-lactam resistant microorganisms, coupled to progress made in genomics, genetics and immunofluorescence microscopy techniques, have encouraged the intensive study of PBPs from a variety of bacterial species.

Crystal structure of penicillin-binding protein 1a (PBP1a) reveals a mutational hotspot implicated in beta-lactam resistance in Streptococcus pneumoniae.

Streptococcus pneumoniae is a major human pathogen whose infections have been treated with beta-lactam antibiotics for over 60 years, but the proliferation of strains that are highly resistant to such drugs is a problem of worldwide concern. Beta-lactams target penicillin-binding proteins (PBPs), membrane-associated enzymes that play essential roles in the peptidoglycan biosynthetic process. Bifunctional PBPs catalyze both the polymerization of glycan chains (glycosyltransfer) and the cross-linking of adjacent pentapeptides (transpeptidation), while monofunctional enzymes catalyze only the latter reaction.

Identical penicillin-binding domains in penicillin-binding proteins of Streptococcus pneumoniae clinical isolates with different levels of beta-lactam resistance.

We have sequenced the penicillin-binding domains of the complete repertoire of penicillin-binding proteins and MurM from 22 clinical isolates of Streptococcus pneumoniae that span a wide range of beta-lactam resistance levels. Evidence of mosaicism was found in the genes encoding PBP 1a, PBP 2b, PBP 2x, MurM, and, possibly, PBP 2a. Five isolates were found to have identical PBP and MurM sequences, even though the MICs for penicillin G ranged from 0.

Crystal structure of phosphorylcholine esterase domain of the virulence factor choline-binding protein e from streptococcus pneumoniae: new structural features among the metallo-beta-lactamase superfamily.

Streptococcus pneumoniae is the worldwide leading cause of deaths from invasive infections such as pneumoniae, sepsis, and meningitidis in children and the elderly. Nasopharyngeal colonization, which plays a key role in the development of pneumococcal disease, is highly dependent on a family of surface-exposed proteins, the choline-binding proteins (CBPs). Here we report the crystal structure of phosphorylcholine esterase (Pce), the catalytic domain of choline-binding protein E (CBPE), which has been shown to be crucial for host/pathogen interaction processes.

The PECACE domain: a new family of enzymes with potential peptidoglycan cleavage activity in Gram-positive bacteria.

Background: The metabolism of bacterial peptidoglycan is a dynamic process, synthases and cleavage enzymes are functionally coordinated. Lytic Transglycosylase enzymes (LT) are part of multienzyme complexes which regulate bacterial division and elongation. LTs are also involved in peptidoglycan turnover and in macromolecular transport systems.

In vitro reconstitution of a trimeric complex of DivIB, DivIC and FtsL, and their transient co-localization at the division site in Streptococcus pneumoniae.

DivIB, DivIC and FtsL are bacterial proteins essential for cell division, which show interdependencies for their stabilities and localization. We have reconstituted in vitro a trimeric complex consisting of the recombinant extracellular domains of the three proteins from Streptococcus pneumoniae. The extracellular domain of DivIB was found to associate with a heterodimer of those of DivIC and FtsL.

Active site restructuring regulates ligand recognition in class A penicillin-binding proteins.

Bacterial cell division is a complex, multimolecular process that requires biosynthesis of new peptidoglycan by penicillin-binding proteins (PBPs) during cell wall elongation and septum formation steps. Streptococcus pneumoniae has three bifunctional (class A) PBPs that catalyze both polymerization of glycan chains (glycosyltransfer) and cross-linking of pentapeptidic bridges (transpeptidation) during the peptidoglycan biosynthetic process. In addition to playing important roles in cell division, PBPs are also the targets for beta-lactam antibiotics and thus play key roles in drug-resistance mechanisms.

Crystal structure of a peptidoglycan synthesis regulatory factor (PBP3) from Streptococcus pneumoniae.

Penicillin-binding proteins (PBPs) are membrane-associated enzymes which perform critical functions in the bacterial cell division process. The single d-Ala,d-Ala (d,d)-carboxypeptidase in Streptococcus pneumoniae, PBP3, has been shown to play a key role in control of availability of the peptidoglycal substrate during cell growth. Here, we have biochemically characterized and solved the crystal structure of a soluble form of PBP3 to 2.

A metallo-beta-lactamase enzyme in action: crystal structures of the monozinc carbapenemase CphA and its complex with biapenem.

One strategy developed by bacteria to resist the action of beta-lactam antibiotics is the expression of metallo-beta-lactamases. CphA from Aeromonas hydrophila is a member of a clinically important subclass of metallo-beta-lactamases that have only one zinc ion in their active site and for which no structure is available. The crystal structures of wild-type CphA and its N220G mutant show the structural features of the active site of this enzyme, which is modeled specifically for carbapenem hydrolysis.

Crystal structure of human otubain 2.

Ubiquitylation, the modification of cellular proteins by the covalent attachment of ubiquitin, is critical for diverse biological processes including cell cycle progression, signal transduction and stress response. This process can be reversed and regulated by a group of proteases called deubiquitylating enzymes (DUBs). Otubains are a recently identified family of DUBs that belong to the ovarian tumour (OTU) superfamily of proteins.

Biochemical characterization of Streptococcus pneumoniae penicillin-binding protein 2b and its implication in beta-lactam resistance.

Extensive use of beta-lactam antibiotics has led to the selection of pathogenic streptococci resistant to beta-lactams due to modifications of the penicillin-binding proteins (PBPs). PBP2b from Streptococcus pneumoniae is a monofunctional (class B) high-molecular-weight PBP catalyzing the transpeptidation between adjacent stem peptides of peptidoglycan. The transpeptidase domain of PBP2b isolated from seven clinical resistant (CR) strains contains 7 to 44 amino acid changes over the sequence of PBP2b from the R6 beta-lactam-sensitive strain.

The D,D-carboxypeptidase PBP3 organizes the division process of Streptococcus pneumoniae.

Bacterial division requires the co-ordination of membrane invagination, driven by the constriction of the FtsZ-ring, and concomitant cell wall synthesis, performed by the high-molecular-weight penicillin-binding proteins (HMW PBPs). Using immunofluorescence techniques, we show in Streptococcus pneumoniae that this co-ordination requires PBP3, a D,D-carboxypeptidase that degrades the substrate of the HMW PBPs. In a mutant deprived of PBP3, the apparent rings of HMW PBPs and that of FtsZ are no longer co-localized.

A PBP2x from a clinical isolate of Streptococcus pneumoniae exhibits an alternative mechanism for reduction of susceptibility to beta-lactam antibiotics.

The human pathogen Streptococcus pneumoniae is one of the main causative agents of respiratory tract infections. At present, clinical isolates of S. pneumoniae often exhibit decreased susceptibility toward beta-lactams, a phenomenon linked to multiple mutations within the penicillin-binding proteins (PBPs).