Bacterial resistance to β-lactams, the most commonly used class of antibiotics, poses a global challenge. This resistance is caused by the production of bacterial enzymes that are termed β-lactamases (βLs). The evolution of serine-class A β-lactamases from penicillin-binding proteins (PBPs) is related to the formation of the Ω-loop at the entrance to the enzyme’s active site. In this loop, the Glu166 residue plays a key role in the two-step catalytic cycle of hydrolysis. This residue in TEM–type β-lactamases, together with Asn170, is involved in the formation of a hydrogen bonding network with a water molecule, leading to the deacylation of the acyl–enzyme complex and the hydrolysis of the β-lactam ring of the antibiotic. The activity exhibited by the Ω-loop is attributed to the positioning of its N-terminal residues near the catalytically important residues of the active site. The structure of the Ω-loop of TEM-type β-lactamases is characterized by low mutability, a stable topology, and structural flexibility. All of the revealed features of the Ω-loop, as well as the mechanisms related to its involvement in catalysis, make it a potential target for novel allosteric inhibitors of β-lactamases.

The microbial resistance to antibiotics is a genuine global threat. Consequently, a search of new inhibitors remains of acute importance due to the increasing spread of multidrug resistance. Here we present a new type of non-beta-lactam beta-lactamase inhibitor PA-34 based on natural phenoxyaniline, identified using computer-assisted screening of scaffolds related to those of known low-affinity inhibitors. The compound displays reversible competitive inhibition of bacterial beta-lactamase TEM-171, with a K-i of 88 mu M. Using enzyme kinetics, infra-red spectroscopy, fluorescence quenching and computer docking, we propose that the inhibitor binds at the entrance to the enzyme active site. This is a novel inhibition mechanism compared to binding covalently to the catalytic serine in the active site or non-covalently to the allosteric site. The residues involved in binding the inhibitor are conserved among molecular class A beta-lactamases. The identified compound and its proposed binding mode may have a potential for a regulation of the catalytic activity of a wide range of class A beta-lactamases. We also hypothesise that the presented route for finding non-beta-lactam compounds may be an effective and durable approach for combating bacterial antibiotic resistance. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

A simple method for the rapid determination of prostate-specific antigen (PSA) in serum is reported using a lateral flow immunoassay with gold nanoparticles as the label. The method uses the intensity of colored test lines to determine PSA from 0.3 to 30 ng/mL. The limit of detection was 0.3 ng/mL and the coefficient of variation was less than 10%. The analysis time was approximately 20 min. The novel method showed good correlation with enzyme linked immunosorbent assay (ELISA) measurements of prostate-specific antigen concentration in human serum with a linear regression coefficient of 0.985. The developed system was stable for at least 12 months when stored from +4 to 30°C and has potential application for clinical practice.