Search

The SARS-CoV-2 papain-like protease (PL pro ) is an antiviral drug target that catalyzes the hydrolysis of the viral polyproteins pp1a/1ab, so releasing the non-structural proteins (nsps) 1-3 that are essential for the coronavirus lifecycle. The LXGG↓X motif in pp1a/1ab is crucial for recognition and cleavage by PL pro . We describe molecular dynamics, docking, and quantum mechanics/molecular mechanics (QM/MM) calculations to investigate how oligopeptide substrates derived from the viral polyprotein bind to PL pro . The results reveal how the substrate sequence affects the efficiency of PL pro -catalyzed hydrolysis. In particular, a proline at the P2' position promotes catalysis, as validated by residue substitutions and mass spectrometry-based analyses. Analysis of PL pro catalyzed hydrolysis of LXGG motif-containing oligopeptides derived from human proteins suggests that factors beyond the LXGG motif and the presence of a proline residue at P2' contribute to catalytic efficiency, possibly reflecting the promiscuity of PL pro . The results will help in identifying PL pro substrates and guiding inhibitor design., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

The SARS-CoV-2 main protease (M pro ) plays an essential role in the coronavirus lifecycle by catalyzing hydrolysis of the viral polyproteins at specific sites. M pro is the target of drugs, such as nirmatrelvir, though resistant mutants have emerged that threaten drug efficacy. Despite its importance, questions remain on the mechanism of how M pro binds its substrates. Here, we apply dynamical nonequilibrium molecular dynamics (D-NEMD) simulations to evaluate structural and dynamical responses of M pro to the presence and absence of a substrate. The results highlight communication between the M pro dimer subunits and identify networks, including some far from the active site, that link the active site with a known allosteric inhibition site, or which are associated with nirmatrelvir resistance. They imply that some mutations enable resistance by altering the allosteric behavior of M pro . More generally, the results show the utility of the D-NEMD technique for identifying functionally relevant allosteric sites and networks including those relevant to resistance., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The main protease (M pro ) of SARS-CoV-2 is central to viral maturation and is a promising drug target, but little is known about structural aspects of how it binds to its 11 natural cleavage sites. We used biophysical and crystallographic data and an array of biomolecular simulation techniques, including automated docking, molecular dynamics (MD) and interactive MD in virtual reality, QM/MM, and linear-scaling DFT, to investigate the molecular features underlying recognition of the natural M pro substrates. We extensively analysed the subsite interactions of modelled 11-residue cleavage site peptides, crystallographic ligands, and docked COVID Moonshot-designed covalent inhibitors. Our modelling studies reveal remarkable consistency in the hydrogen bonding patterns of the natural M pro substrates, particularly on the N-terminal side of the scissile bond. They highlight the critical role of interactions beyond the immediate active site in recognition and catalysis, in particular plasticity at the S2 site. Building on our initial M pro -substrate models, we used predictive saturation variation scanning (PreSaVS) to design peptides with improved affinity. Non-denaturing mass spectrometry and other biophysical analyses confirm these new and effective 'peptibitors' inhibit M pro competitively. Our combined results provide new insights and highlight opportunities for the development of M pro inhibitors as anti-COVID-19 drugs., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The main viral protease (Mpro) of SARS-CoV-2 is a nucleophilic cysteine hydrolase and a current target for anti-viral chemotherapy. We describe a high-throughput solid phase extraction coupled to mass spectrometry Mpro assay. The results reveal some β-lactams, including penicillin esters, are active site reacting Mpro inhibitors, thus highlighting the potential of acylating agents for Mpro inhibition.

An important mechanism of resistance to β-lactam antibiotics is via their β-lactamase-catalyzed hydrolysis. Recent work has shown that, in addition to the established hydrolysis products, the reaction of the class D nucleophilic serine β-lactamases (SBLs) with carbapenems also produces β-lactones. We report studies on the factors determining β-lactone formation by class D SBLs. We show that variations in hydrophobic residues at the active site of class D SBLs ( i.e. Trp 105 , Val 120 , and Leu 158 , using OXA-48 numbering) impact on the relative levels of β-lactones and hydrolysis products formed. Some variants, i.e. the OXA-48 V120L and OXA-23 V128L variants, catalyze increased β-lactone formation compared with the WT enzymes. The results of kinetic and product studies reveal that variations of residues other than those directly involved in catalysis, including those arising from clinically observed mutations, can alter the reaction outcome of class D SBL catalysis. NMR studies show that some class D SBL variants catalyze formation of β-lactones from all clinically relevant carbapenems regardless of the presence or absence of a 1β-methyl substituent. Analysis of reported crystal structures for carbapenem-derived acyl-enzyme complexes reveals preferred conformations for hydrolysis and β-lactone formation. The observation of increased β-lactone formation by class D SBL variants, including the clinically observed carbapenemase OXA-48 V120L, supports the proposal that class D SBL-catalyzed rearrangement of β-lactams to β-lactones is important as a resistance mechanism., Competing Interests: Conflict of interest—The authors declare that they have no conflicts of interest with the contents of this article., (© 2020 Aertker et al.)

Enzymes often use nucleophilic serine, threonine, and cysteine residues to achieve the same type of reaction; the underlying reasons for this are not understood. While bacterial d,d-transpeptidases (penicillin-binding proteins) employ a nucleophilic serine, l,d-transpeptidases use a nucleophilic cysteine. The covalent complexes formed by l,d-transpeptidases with some β-lactam antibiotics undergo non-hydrolytic fragmentation. This is not usually observed for penicillin-binding proteins, or for the related serine β-lactamases. Replacement of the nucleophilic serine of serine β-lactamases with cysteine yields enzymes which fragment β-lactams via a similar mechanism as the l,d-transpeptidases, implying the different reaction outcomes are principally due to the formation of thioester versus ester intermediates. The results highlight fundamental differences in the reactivity of nucleophilic serine and cysteine enzymes, and imply new possibilities for the inhibition of nucleophilic enzymes., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)