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Kurt Yilmaz, N.

Publications and source records attributed to Kurt Yilmaz, N..

11 recordsLinked to original sources

A Dynamics-Informed Machine Learning Framework for Inhibitor Optimization Against Quickly Evolving Targets to Avoid Resistance

Drug resistance often emerges through mutations that reshape protein conformational ensembles, allowing inhibitor potency to be altered without directly disrupting protein-ligand contacts. Consequently, the molecular mechanisms underlying these effects remain difficult to identify, hindering the design of inhibitors with durable potency against rapidly evolving drug targets. To address this challenge, we developed ROBUST, a physics-informed machine learning framework that integrates experimental measurements, molecular dynamics simulations, and interpretable statistical modeling to identify energetic determinants of inhibitor potency. Using HIV-1 protease as a stringent model system for drug resistance, we determined 157 new inhibition constants and integrated them with prior measurements to establish a comprehensive experimental dataset of 364 protease-inhibitor pairs. Analysis of the corresponding molecular dynamics simulations revealed a compact network of energetic interactions that quantitatively explains how resistance mutations and inhibitor modifications jointly reshape molecular recognition and inhibitor potency across the multidimensional resistance landscape. Models constructed from these energetic signatures predicted binding free energies with high accuracy (RMSE < 1 kcal mol-1) and successfully generalized to unseen darunavir analogs. Importantly, ROBUST accurately prioritized unseen analogs based on their potency across the variant set, demonstrating its utility for identifying compounds with improved resistance profiles. Together, these results uncover the energetic principles through which resistance mutations and inhibitor modifications alter potency and establish ROBUST as a mechanistically interpretable framework for translating these insights into resistance-aware inhibitor optimization against rapidly evolving drug targets.

biophysics↗

Cooperativity and Communication between the Active Sites of the Dimeric SARS-CoV-2 Main Protease

The coronaviral main protease (Mpro) is essential for the replication of the virus, and has been the subject of various biochemical, structural and enzymatic studies, as well as a drug target against SARS-CoV-2 infections. SARS-CoV-2 Mpro is known to be active as a dimer, with the N terminus of one protomer completing a key active site pocket of the other protomer. Despite apparent cooperativity in catalytic activity, how the two distal active sites in the dimer communicate and might be modulating binding and/or catalysis at the other remain to be clarified. Here, we have investigated the interplay between cooperativity, dimerization, and substrate cleavage in SARS-CoV-2 Mpro through a combination of enzymatic assays, crystal structures, and protein characterization. To disentangle the contribution of each active site to the observed enzymatic activity, we developed a cleavage assay involving heterodimers of active and inactive (C145A or inhibitor-bound) monomers. Strikingly, we found that heterodimerization increased cleavage efficiency per active monomer. Additionally, we mapped a network of critical residues bridging the two active sites and probed this network through engineered mutations. By dissecting the cooperativity and communication between the active sites, we provide new insights into the Mpro reaction cycle and functional significance of its dimeric architecture.

biochemistry↗

Molecular Mechanisms of Drug Resistance and Compensation in SARS-CoV-2 Main Protease: The Interplay Between E166 and L50

The SARS-CoV-2 main protease (Mpro) is essential for viral replication, and a primary target for COVID-19 antivirals. Direct-acting antivirals such as nirmatrelvir, the active component of Paxlovid, target the Mpro active site to block viral polyprotein cleavage and thus replication. However, drug resistance mutations at the active site residue Glu166 (E166) have emerged in in vitro selection studies, raising concerns about the durability of current antiviral strategies. Here, we investigate the molecular basis of drug resistance conferred by E166A and E166V mutations against nirmatrelvir and the related PF-00835231, individually and in combination with the distal mutation L50F. We found that E166 mutations reduce nirmatrelvir potency by up to 3000-fold while preserving substrate cleavage, with catalytic efficiency reduced by only up to 2- fold. This loss of catalytic efficiency was compensated for by the addition of L50F in the double- mutant variants. We have determined three cocrystal structures of the E166 variants (E166A, E166V, and E166V/L50F) bound to PF-00835231. Comparison of these structures with wild- type demonstrated that E166 is crucial for dimerization and for shaping the substrate-binding S1 pocket. Our findings highlight the mutability of E166, a prime site for resistance for inhibitors that leverage direct interactions with this position, and the potential emergence of highly resistant and active variants in combination with the compensatory mutation L50F. These insights support the design of inhibitors that target conserved protease features and avoid E166 side- chain interactions to minimize susceptibility to resistance.

biochemistry↗

Next generation APOBEC3 inhibitors: Optimally designed for potency and nuclease stability

APOBEC3 (or A3) enzymes have emerged as potential therapeutic targets due to their role in introducing heterogeneity in viruses and cancer, often leading to drug resistance. Inhibiting these enzymes has remained elusive as initial phosphodiester (PO) linked DNA based inhibitors lack stability and potency. We have enhanced both potency and nuclease stability, of 2'-deoxy-zebularine (dZ), substrate-based oligonucleotide inhibitors for two critical A3s: A3A and A3G. While replacing the phosphate backbone with phosphorothioate (PS) linkages increased nuclease stability, fully PS-modified inhibitors lost potency (1.4-3.7 fold) due to the structural constraints of the active site. For both enzymes, mixed PO/PS backbones enhanced potency (2.3-9.2 fold), while also vastly improving nuclease resistance. We also strategically introduced 2'-fluoro sugar modifications, creating the first nanomolar inhibitor of A3G-CTD2. With hairpin-structured inhibitors containing optimized PS patterns and LNA sugar modifications, we characterize the first single-digit nanomolar inhibitor targeting A3A. These extremely potent A3A inhibitors, were highly resistant to nuclease degradation in serum stability assays. Overall, our optimally designed A3 oligonucleotide inhibitors show improved potency and stability, compared to previous attempts to inhibit these critical enzymes, opening the door to realize the therapeutic potential of A3 inhibition.

biochemistry↗

Systematic analyses of the resistance potential of drugs targeting SARS-CoV-2 main protease

Drugs that target the main protease (Mpro) of SARS-CoV-2 are effective therapeutics that have entered clinical use. Wide-scale use of these drugs will apply selection pressure for the evolution of resistance mutations. To understand resistance potential in Mpro, we performed comprehensive surveys of amino acid changes that can cause resistance in a yeast screen to nirmatrelvir (contained in the drug Paxlovid), and ensitrelvir (Xocova) that is currently in phase III trials. The most impactful resistance mutation (E166V) recently reported in multiple viral passaging studies with nirmatrelvir showed the strongest drug resistance score for nirmatrelvir, while P168R had the strongest resistance score for ensitrelvir. Using a systematic approach to assess potential drug resistance, we identified 142 resistance mutations for nirmatrelvir and 177 for ensitrelvir. Among these mutations, 99 caused apparent resistance to both inhibitors, suggesting a strong likelihood for the evolution of cross-resistance. Many mutations that exhibited inhibitor-specific resistance were consistent with distinct ways that each inhibitor protrudes beyond the substrate envelope. In addition, mutations with strong drug resistance scores tended to have reduced function. Our results indicate that strong pressure from nirmatrelvir or ensitrelvir will select for multiple distinct resistant lineages that will include both primary resistance mutations that weaken interactions with drug while decreasing enzyme function and secondary mutations that increase enzyme activity. The comprehensive identification of resistance mutations enables the design of inhibitors with reduced potential of developing resistance and aids in the surveillance of drug resistance in circulating viral populations.

molecular biology↗

Crystal Structures of Inhibitor-Bound Main Protease from Delta- and Gamma-Coronaviruses

With the spread of SARS-CoV-2 throughout the globe to cause the COVID-19 pandemic, the threat of zoonotic transmissions of coronaviruses (CoV) has become even more evident. As human infections have been caused by alpha- and beta-CoVs, structural characterization and inhibitor design mostly focused on these two genera. However, viruses from the delta and gamma genera also infect mammals and pose potential zoonotic transmission threat. Here, we determined the inhibitor-bound crystal structures of the main protease (Mpro) from the delta-CoV porcine HKU15 and gamma-CoV SW1 from beluga whale. Comparison with the apo structure of SW1 Mpro, which we also present here, enabled identifying structural arrangements upon inhibitor binding at the active site. The binding modes and interactions of two covalent inhibitors, PF-00835231 (lufotrelvir) bound to HKU15 and GC376 bound to SW1 Mpro, reveal features that may be leveraged to target diverse coronaviruses and toward structure-based design of pan-CoV inhibitors.

biochemistry↗

Defining the Substrate Envelope of SARS-CoV-2 Main Protease to Predict and Avoid Drug Resistance

Coronaviruses, as exemplified by SARS-CoV-2, can evolve and spread rapidly to cause severe disease morbidity and mortality. Direct acting antivirals (DAAs) are highly effective in decreasing disease burden especially when they target essential viral enzymes, such as proteases and polymerases, as demonstrated in HIV-1 and HCV and most recently SARS-CoV-2. Optimization of these DAAs through iterative structure-based drug design has been shown to be critical. Particularly, the evolutionarily conserved molecular mechanisms underlying viral replication can be leveraged to develop robust antivirals against rapidly evolving viral targets. The main protease (Mpro) of SARS-CoV-2, which is evolutionarily constrained to recognize and cleave 11 specific sites to promote viral maturation, exemplifies one such target. In this study we define the substrate envelope of Mpro by determining the molecular basis of substrate recognition, through nine high-resolution cocrystal structures of SARS-CoV-2 Mpro with the viral cleavage sites. These structures enable identification of evolutionarily vulnerable sites beyond the substrate envelope that may be susceptible to drug resistance and compromise binding of the newly developed Mpro inhibitors.

biochemistry↗

IgA MAb blocks SARS-CoV-2 Spike-ACE2 interaction providing mucosal immunity

COVID-19 caused by SARS-CoV-2 has become a global pandemic requiring the development of interventions for the prevention or treatment to curtail mortality and morbidity. No vaccine to boost mucosal immunity or as a therapeutic has yet been developed to SARS-CoV-2. In this study we discover and characterize a cross-reactive human IgA monoclonal antibody, MAb362. MAb362 binds to both SARS-CoV and SARS-CoV-2 spike proteins and competitively blocks hACE2 receptor binding, by completely overlapping the hACE2 structural binding epitope. Furthermore, MAb362 IgA neutralizes both pseudotyped SARS-CoV and SARS-CoV-2 in human epithelial cells expressing hACE2. SARS-CoV-2 specific IgA antibodies, such as MAb362, may provide effective immunity against SARS-CoV-2 by inducing mucosal immunity within the respiratory system, a potentially critical feature of an effective vaccine.

microbiology↗

Structural Adaptation of Darunavir Analogs Against Primary Resistance Mutations in HIV-1 Protease

HIV-1 protease is one of the prime targets of agents used in antiretroviral therapy against HIV. However, under selective pressure of protease inhibitors, primary mutations at the active site weaken inhibitor binding to confer resistance. Darunavir (DRV) is the most potent HIV-1 protease inhibitor in clinic; resistance is limited, as DRV fits well within the substrate envelope. Nevertheless, resistance is observed due to hydrophobic changes at residues including I50, V82 and I84 that line the S1/S1 pocket within the active site. Through enzyme inhibition assays and a series of 12 crystal structures, we interrogated susceptibility of DRV and two potent analogs to primary S1 mutations. The analogs had modifications at the hydrophobic P1 moiety to better occupy the unexploited space in the S1 pocket where the primary mutations were located. Considerable losses of potency were observed against protease variants with I84V and I50V mutations for all three inhibitors. The crystal structures revealed an unexpected conformational change in the flap region of I50V protease bound to the analog with the largest P1 moiety, indicating interdependency between the S1 subsite and the flap region. Collective analysis of protease-inhibitor van der Waals (vdW) interactions in the crystal structures using principle component analysis indicated I84V mutation underlying the largest variation in the vdW contacts. Interestingly, the principle components were able to distinguish inhibitor identity and relative potency solely based on vdW interactions of active site residues in the crystal structures. Our results reveal the interplay between inhibitor P1 moiety and primary S1 mutations, as well as suggesting a novel method for distinguishing the interdependence of resistance through principle component analyses.

molecular biology↗

Structural analysis of the active site and DNA binding of human cytidine deaminase APOBEC3B

APOBEC3s proteins (A3s), a family of human cytidine deaminases, protect the host cell from endogenous retro-elements and exogenous viral infections by introducing hypermutations. However, the ability to mutate genomic DNA makes A3s a potential cancer source. Of the 7 human A3s, A3B has been implicated as an endogenous cause for multiple cancers. Despite overall similarity, A3s have distinct deamination activity with A3B among the least catalytically active. Over the past few years, several structures of apo as well as DNA-bound A3 proteins have been determined. These structures revealed the molecular determinants of nucleotide specificity and the importance of the loops around the active site in DNA binding. However, for A3B, the structural basis for regulation of deamination activity and the role of active site loops in coordinating DNA had remained unknown. In this study, using a combination of advanced molecular modelling followed by experimental mutational analysis and dynamics simulations, we investigated molecular mechanism of A3B regulating activity and DNA binding. We identified a unique auto-inhibited conformation of A3B that restricts access and binding of DNA to the active site, mainly due to the extra PLV residues in loop 1. We modelled DNA binding to fully native A3B and found that Arg211 in the arginine patch of loop1 is the gatekeeper while Arg212 stabilizes the bound DNA. This model also identified the critical residues for substrate specificity, especially at the -1 position. Our results reveal the structural basis for relatively lower catalytic activity of A3B and provide opportunities for rational design of inhibitors that specifically target A3B to benefit cancer therapeutics.

biochemistry↗

Substrate sequence selectivity of APOBEC3A implicates intra-DNA interactions

The APOBEC3 (A3) family of human cytidine deaminases is renowned for providing a first line of defense against many exogenous and endogenous retroviruses. However, the ability of these proteins to deaminate deoxycytidines in ssDNA makes A3s a double-edged sword. When overexpressed, A3s can mutate endogenous genomic DNA resulting in a variety of cancers. Although the sequence context for mutating DNA varies among A3s, the mechanism for substrate sequence specificity is not well understood. To characterize substrate specificity of A3A, a systematic approach was used to quantify the affinity for substrate as a function of sequence context, length, substrate secondary structure, and pH. We identified the A3A ssDNA binding motif as (T/C)TC(A/G), and found that A3A binds RNA in a sequence specific manner. Furthermore, A3A bound tighter to its substrate binding motif when in a loop compared to linear oligonucleotide. Our results suggest that the A3A affinity and preference for substrate is modulated by the structure of DNA, and not just its chemical identity. Analysis of previously published co-crystal structures of A3A bound to ssDNA in light of the above findings directed the proposal of a new model for the molecular mechanism underlying A3A sequence preference. On a broader scale, the results of this work not only provide key insights into the mechanism of A3s beneficial roles in the cell, especially in viral restriction, but also into A3s deleterious activity such as in the development of cancer.

biochemistry↗