Dmitry Lyumkis

The encapsulation of the viral RNA condensate inside the capsid is a crucial step in the late stages of the HIV-1 replication cycle. While it is agreed that RNA encapsulation depends on RNA-bound integrase (IN), that capsid-bound IN-RNA filaments are present within the capsid, and that the ribonucleoprotein (RNP) complex takes up only a fraction of the capsid volume, the timing of filament formation and ribonucleoprotein (RNP) encapsulation are unclear. Here, we ran virion-scale, coarse grained molecular dynamics simulations to identify how the organization of the RNP and IN in particular affects mature capsid assembly and genome encapsulation. These virion-scale simulations allow for direct comparison between experimental capsid morphologies and those self-assembled in the simulations. It was found, when relatively few tetramers are on the RNP surface, that IN tetramers could facilitate RNA encapsulation without filling a significant fraction of the capsid volume, but do not form a capsid-templated filament. When octameric IN-RNA filaments are modeled, it was found that WT-like capsid morphologies form only when the IN is organized as a single long filament, in agreement with recent experimental suggestions. These capsids are more conical and elongated than the capsids assembled around the RNP with tetrameric IN. Thus, we suggest the IN-RNA filament assembles ahead of the capsid and directs it to its final conical morphology, consistent with the experimental observation of less elongated capsids when IN oligomerization is disrupted.

Expanded genetic alphabets with synthetic nucleotides can greatly increase the chemical diversity of nucleic acids, enabling new molecular functions. Because cellular transcription is executed by multi-subunit RNA polymerases, the compatibility of unnatural base pairs with this machinery is essential for engineering expanded genetic systems. Here we demonstrate that Escherichia coli RNA polymerase efficiently transcribes an eight-letter genetic alphabet with two orthogonal unnatural base pairs: P:Z and B:S pairs. To overcome G:Z misincorporation, we synthesize a higher-fidelity analogue, termed Z*, in which the C5 nitro group is replaced with a carboxamide. To elucidate substrate-recognition mechanisms, we determine four cryo-electron microscopy structures of RNA polymerase incorporating dZ:PTP or dP:Z*TP at 2.42–2.75 Å resolution. These structures, together with our early work on S:B pair, show that E. coli RNA polymerase is able to efficiently recognize these unnatural base pairs in the same manner as natural base pairs. Collectively, these results establish the feasibility of an eight-letter genetic alphabet for transcription.

Life began with the emergence of a molecule that could replicate its own genetic material, a task plausibly mediated by an RNA-dependent RNA polymerase ribozyme. Here, we present the structure of such a polymerase ribozyme, bound to RNA substrates comprising the template, primer, and nucleoside triphosphate (NTP) analog. The structure reveals how directed evolution shaped flanking elements around a highly conserved catalytic core derived from the ancestral class I ligase ribozyme. Each element serves as a functional module, positioning the primer-template duplex and incoming NTP within the active site of the enzyme. This emergent domain organization is remarkably similar to the “right hand” configuration of polymerase proteins, suggesting a common functional form for copying nucleic acids, regardless of biopolymer catalyst.

Glutamate dehydrogenase (GDH) is a highly regulated key enzyme that catalyzes the reversible oxidative deamination of glutamate to α-ketoglutarate, positioning it at a critical hub linking amino acid catabolism to energy production while supplying ammonia for urea synthesis and other nitrogen pathways. Early investigations have shown that bovine GDH (bGDH), which shares 98% sequence identity with its human homolog, assembles into polymeric filaments with altered allosteric responses. Filamentation has only relatively recently been appreciated as a widespread mechanism of enzyme regulation, prompting a reevaluation of these early observations in GDH. Here, we use high-resolution cryogenic electron microscopy (cryo-EM) to show that bGDH hexamers assemble via reciprocal “antenna” interactions that oppose the conformational changes associated with GTP inhibition, revealing how filamentation reshapes GDH allostery and with implications for the treatment of human disease.

Cell-cell transmission of HIV-1 (CCT) is a highly efficient mode of intrahost transmission that provides viral particles broad protection from antiretroviral agents including antiretroviral drugs, host restriction factors, and broadly neutralizing antibodies. Interestingly, the exact factors that grant viral particles increased protection and efficiency during intrahost spread remain unclear. Using a T cell co-culturing system and correlative cryoelectron tomography (cryoET) workflow, we investigated the architecture of HIV-1 CCT sites in a near-native, in situ context to address why CCT is efficient and grants this resistance. Contrary to previous models which suggest large, virus-packed sites, our 3D reconstructions reveal that CCT occurs within small intercellular spaces containing on average 1–5 viral particles. Surrounding these spaces are long, tight membrane interfaces that seclude the viral particles from the remaining extracellular environment. These observations suggest a model where spatial isolation may limit accessibility of antiretroviral agents to the virus-containing spaces thereby conferring protection to viral particles during transmission. To functionally validate these structural insights, we developed a quantitative flow cytometry strategy that decouples CCT conjugate formation from successful CCT infection through the analysis of multicell events. This methodology allows us to systematically compare the impact different molecules such as Env and CD4 have on HIV-1 CCT in a quantitative and population-level manner. Using this approach, we determined that initial HIV-1 CCT conjugate formation is partially dependent on CD4, but the Env involved in conjugate formation may differ from Env used for viral entry. Overall, these findings may prompt a rethinking of intervention strategies for HIV-1 CCT and have further implications with cytoplasmic trafficking, nuclear import, and host restriction factors.

HIV-1 integrase (IN) strand transfer inhibitors (INSTIs) are central to modern antiretroviral therapy (ART) because of their high potency and durable effect on viral suppression. However, drug resistance mutations (DRMs) within HIV-1 IN emerge, which can compromise long-term treatment efficacy. Many distinct DRMs that arise under INSTI therapy have been extensively tabulated in public repositories and literature. However, the timelines over which they emerge, accumulate, and consolidate in patients have not been systematically integrated across clinical and experimental studies. In this review, we synthesize current evidence on the temporal evolution of DRMs within HIV-1 IN by examining mutational kinetic data from viruses derived from people living with HIV/AIDS (PLWH) and from in vitro selection experiments. We compare experimental timelines to recent computational predictions derived from Potts-based fitness landscapes coupled with kinetic Monte Carlo simulations and identify reproducible kinetic classes that distinguish fast-, intermediate-, and slow-emerging DRMs. Rapidly emerging DRMs such as E92Q and N155H typically appear early under drug pressure and often represent low-barrier adaptive responses, whereas the most clinically consequential mutations, such as Q148H/K/R, G140A/S, and E138K, arise only after extended therapy and generally require compensatory mutational backgrounds to persist. Although absolute emergence times vary substantially between in vivo and in vitro systems, consistent temporal trends across datasets support the existence of underlying epistatic constraints that shape drug resistance evolution. Understanding DRM timelines is clinically relevant because it provides a framework for interpreting resistance detected at virological failure, informs optimal timing of resistance testing, and may enable earlier identification of high-risk evolutionary trajectories before durable resistance is established.

Histidine phosphorylation is a non-canonical post-translational modification (PTM), with 1-phosphohistidine (1-pHis) and 3-phosphohistidine (3-pHis) isoforms, that is understudied due to a lack of robust reagents, including high-affinity pHis-specific antibodies. Engineering pHis antibodies is challenging due to the labile nature of its phosphoramidate (P-N) bond. We developed a strategy for in vitro engineering of antibodies for the detection of native 3-pHis targets, in which the rabbit SC44-8 anti-3-pTza mAb is humanized into a scaffold (hSC44) that is suitable for phage display. Six unique Fab phage-displayed hSC44 scaffold libraries were screened for antibodies that bound 3-pHis with higher affinity and had specificity for 3-pHis versus 3-pTza. hSC44.20N32F ^L , the best engineered antibody, has ~10-fold higher affinity for 3-pHis than parental hSC44. Eleven new Fab structures, including the first antibody-pHis peptide structures, together with structural and quantum mechanical calculations, provided molecular insights into 3-pHis and 3-pTza discrimination by hSC44.20N32F ^L and the increased affinity obtained through engineering. We demonstrated the utility of these high-affinity 3-pHis-specific antibodies for the recognition of pHis proteins in mammalian cells by immunoblotting and immunofluorescence staining. Our work describes a general method for engineering labile PTM-specific antibodies and provides novel antibodies for investigating the role of 3-pHis in cell biology.

Integrase (IN) performs dual essential roles during HIV-1 replication. During ingress, IN functions within an oligomeric “intasome” assembly to catalyze viral DNA integration into host chromatin. During late stages of infection, tetrameric IN binds viral RNA and orchestrates the condensation of ribonucleoprotein complexes into the capsid core. The molecular architectures of HIV-1 IN assemblies that mediate these distinct events remain unknown. Furthermore, the IN tetramer is an important antiviral target for investigational allosteric IN inhibitors. Here, we determined cryo-EM structures of wildtype HIV-1 IN tetramers and intasome hexadecamers. Our structures unveil a remarkable plasticity that leverages IN C-terminal domains and abutting linkers to assemble functionally distinct oligomeric forms. Alteration of a newly recognized conserved interface revealed that both IN functions track with tetramerization in vitro and during HIV-1 infection. Collectively, our findings reveal how IN plasticity orchestrates its diverse molecular functions and suggest a working model for IN-viral RNA binding. Moreover, our structure of the IN tetramer provides atomic blueprints for the rational development of improved allosteric inhibitors.

Drug resistance remains a significant obstacle to identifying effective treatments for HIV-1 infection. Integrase strand transfer inhibitors (INSTIs) are frontline treatments used in combination antiretroviral therapy, but their efficacy can be compromised by emergence of resistance-associated mutations. The development of compounds that will retain efficacy against drug-resistant variants is of significant interest. Herein, we report the synthesis of naphthyridine-based INSTIs with a combination of 4-amino and 5-hydroxymethyl groups. Comparison of the resistance mutant profiles of the new compounds with FDA-approved second-generation INSTIs showed that the lead compounds are comparable to or surpass the efficacy of clinically used drugs against some of the most prevalent drug-resistant mutations that emerge in patient-derived viral isolates. High-resolution cryogenic electron microscopy (cryo-EM) structures of HIV-1 intasomes with two of the best naphthyridine-based INSTIs bound highlight how these inhibitors make enhanced interactions with viral DNA, particularly through optimized DNA stacking. Molecular dynamics simulations together with quantum mechanical and molecular mechanical calculations indicate that the interplay between intramolecular bonding, stacking geometry, resonance effects, and charge distribution governs drug binding within the active site of the intasome. The data mechanistically explain how key interactions contribute to improved antiviral potency against drug-resistant mutants and highlight a new strategy to combat HIV-1 resistance.