Biology subjects

Rubinstein, J. L.

Publications and source records attributed to Rubinstein, J. L..

At least 37 records · Page 2Linked to original sources

bioRxiv2022

Antibody avidity and multi-specificity combined to confer protection against SARS-CoV-2 and resilience against viral escape

SARS-CoV-2, the causative agent of COVID-19, has been responsible for a global pandemic. Monoclonal antibodies have been used as antiviral therapeutics, but have been limited in efficacy by viral sequence variability in emerging variants of concern (VOCs), and in deployment by the need for high doses. In this study, we leverage the MULTI-specific, multi-Affinity antiBODY (Multabody, MB) platform, derived from the human apoferritin protomer, to drive the multimerization of antibody fragments and generate exceptionally potent and broad SARS-CoV-2 neutralizers. CryoEM revealed a high degree of homogeneity for the core of these engineered antibody-like molecules at 2.1 [A] resolution. We demonstrate that neutralization potency improvements of the MB over corresponding IgGs translates into superior in vivo protection: in the SARS-CoV-2 mouse challenge model, comparable in vivo protection was achieved for the MB delivered at 30x lower dose compared to the corresponding IgGs. Furthermore, we show how MBs potently neutralize SARS-CoV-2 VOCs by leveraging augmented avidity, even when corresponding IgGs lose their ability to neutralize potently. Multiple mAb specificities could also be combined into a single MB molecule to expand the neutralization breadth beyond SARS-CoV-2 to other sarbecoviruses. Our work demonstrates how avidity and multi-specificity combined can be leveraged to confer protection and resilience against viral diversity that exceeds that of traditional monoclonal antibody therapies.

immunology↗

bioRxiv2022

Structural basis of V-ATPase VO region assembly by Vma12p, 21p, and 22p

Vacuolar-type ATPases (V-ATPases) are rotary proton pumps that acidify specific intracellular compartments in almost all eukaryotic cells. These multi-subunit enzymes consist of a soluble catalytic V1 region and a membrane-embedded proton-translocating VO region. VO is assembled in the endoplasmic reticulum (ER) membrane and V1 is assembled in the cytosol. However, V1 binds VO only after VO is transported to the Golgi membrane, thereby preventing acidification of the ER. We isolated VO complexes and subcomplexes from Saccharomyces cerevisiae bound to V-ATPase assembly factors Vma12p, Vma21p, and Vma22p. Electron cryomicroscopy shows how the Vma12-22p complex recruits subunits a, e, and f to the rotor ring of VO while blocking premature binding of V1. Vma21p, which contains an ER-retrieval motif, binds the VO:Vma12-22p complex, mature VO, and a complex that appears to contain a ring of loosely-packed rotor subunits and the proteins YAR027W and YAR028W. The structures suggest that Vma21p binds assembly intermediates that contain a rotor ring, and that activation of proton pumping following assembly of V1 with VO removes Vma21p, allowing V-ATPase to remain in the Golgi. Together, these structures show how Vma12-22p and Vma21p function in V-ATPase assembly and quality control, ensuring the enzyme acidifies only its intended cellular targets.

biochemistry↗

bioRxiv2022

Structure of mycobacterial respiratory Complex I

Oxidative phosphorylation, the combined activity of the electron transport chain (ETC) and adenosine triphosphate synthase, has emerged as a valuable target for the treatment of infection by Mycobacterium tuberculosis and other mycobacteria. The mycobacterial ETC is highly branched with multiple dehydrogenases transferring electrons to a membrane-bound pool of menaquinone and multiple oxidases transferring electrons from the pool. The proton-pumping type I nicotinamide adenine dinucleotide (NADH) dehydrogenase (Complex I) is found at low abundance in the plasma membranes of mycobacteria in typical in vitro culture conditions and is often considered dispensable. We found that growth of Mycobacterium smegmatis in carbon-limited conditions greatly increased the abundance of Complex I and allowed isolation of a rotenone-sensitive preparation of the enzyme. Determination of the structure of the complex by cryoEM revealed the "orphan" two-component response regulator protein MSMEG_2064 as a subunit of the assembly. MSMEG_2064 in the complex occupies a site similar to the proposed redox sensing subunit NDUFA9 in eukaryotic Complex I. An apparent purine nucleoside triphosphate within the NuoG subunit resembles the GTP-derived molybdenum cofactor in homologous formate dehydrogenase enzymes. The membrane region of the complex binds acyl phosphatidylinositol dimannoside, a characteristic three-tailed lipid from the mycobacterial membrane. The structure also shows menaquinone, which is preferentially used over ubiquinone by gram-positive bacteria, in two different positions along the quinone channel and suggests that menaquinone interacts more extensively than ubiquinone with a key catalytic histidine residue in the enzyme.

biochemistry↗

bioRxiv2022

Structure of V-ATPase from citrus fruit

Vacuolar-type ATPases (V-ATPases) are rotary proton pumps involved in numerous essential cellular processes in all eukaryotes. Difficulty in obtaining preparations of purified V-ATPase from plants in sufficient quantities for structural analysis has hindered determining the 3D structure of the plant V-ATPase. We used the Legionella pneumophila effector SidK to affinity-purify the endogenous V-ATPase from lemon fruit. The preparation was sufficient to partially cover an electron microscopy specimen grid, allowing structure determination for the enzyme in two rotational states. The structure defines the ATP:H+ ratio of the enzyme, demonstrating that it can establish a maximum {Delta}pH of [~]3, which is insufficient to maintain the low pH observed in the vacuoles of juice sac cells in lemons and other citrus fruit. Compared to the yeast and mammalian enzymes, the membrane region of the plant V-ATPase lacks subunit f and possesses an unusual configuration of transmembrane helices. Subunit H, which inhibits ATP hydrolysis in the isolated catalytic region of V-ATPase, adopts two different conformations in the intact complex, hinting at a role in modulating activity in the intact enzyme.

biochemistry↗

bioRxiv2022

Structural basis of mammalian Complex IV inhibition by steroids

The mitochondrial electron transport chain maintains the proton motive force that powers ATP synthesis. The energy for this process comes from oxidation of NADH and succinate, with the electrons from this oxidation passed via intermediate carriers to oxygen. Complex IV (CIV), the terminal oxidase, transfers electrons from the intermediate electron carrier cytochrome c to oxygen, contributing to the proton motive force in the process. Within CIV, protons move through the K- and D-pathways during turnover. The former is responsible for transferring two protons to the enzymes catalytic site upon reduction of the site, where they eventually combine with oxygen and electrons to form water. CIV is the main site for respiratory regulation, and although previous studies showed that steroid-binding can regulate CIV activity little is known about how this regulation occurs. Here we characterize the interaction between CIV and steroids using a combination of kinetic experiments, structure determination, and molecular simulations. We show that molecules with a sterol moiety, such as glyco-diosgenin and cholesteryl hemisuccinate, reversibly inhibit CIV. Flash photolysis experiments probing the high-speed equilibration of electrons within CIV demonstrate that binding of these molecules inhibits proton uptake through the K-pathway. Single particle cryo-EM of CIV with glyco-diosgenin reveals a previously undescribed steroid-binding site adjacent to the K-pathway, and molecular simulations suggest that the steroid binding modulates the conformational dynamics of key residues and proton transfer kinetics within this pathway. The binding pose of the sterol group sheds light on possible structural gating mechanisms in the CIV catalytic cycle. SIGNIFICANCE STATEMENTMammalian complex IV (CIV), the final complex of the mitochondrial electron transport chain, uses electrons from cytochrome c to reduce oxygen to water, driving aerobic life. Although CIV functions as the main site for respiratory regulation, there is little structural or biochemical information on how this regulation occurs. Previous studies provided evidence of CIV regulation by steroids, but the steroid binding site and regulatory mechanism remain unclear. Using single particle cryogenic electron microscopy, we discover the binding site of the steroid-derived detergent, glyco-diosgenin. Results from flash photolysis kinetic experiments with CIV in the presence of glyco-diosgenin and cholesterol hemisuccinate are combined with cryo-EM and molecular simulations to elucidate how steroid binding limits proton uptake by the complex.

biophysics↗

bioRxiv2022

Structure of ATP synthase under strain during catalysis

ATP synthases are macromolecular machines consisting of an ATP-hydrolysis-driven F1 motor and a proton-translocation-driven FO motor. The F1 and FO motors oppose each others action on a shared rotor subcomplex and are held stationary relative to each other by a peripheral stalk. Structures of resting mitochondrial ATP synthases revealed a left-handed curvature of the peripheral stalk even though rotation of the rotor, driven by either ATP hydrolysis in F1 or proton translocation through FO, would apply a right-handed bending force to the stalk. We used cryoEM to image yeast mitochondrial ATP synthase under strain during ATP-hydrolysis-driven rotary catalysis, revealing a large deformation of the peripheral stalk. The structures show how the peripheral stalk opposes the bending force and suggests that proton translocation during ATP synthesis causes accumulation of strain in the stalk, which relaxes by driving the relative rotation of the rotor through six sub-steps within F1, leading to catalysis.

biophysics↗

bioRxiv2021

Cryo-EM of the yeast VO complex reveals distinct binding sites for macrolide V-ATPase inhibitors

Vacuolar-type adenosine triphosphatases (V-ATPases) are proton pumps found in almost all eukaryotic cells. These enzymes consist of a soluble catalytic V1 region that hydrolyzes ATP and a membrane-embedded VO region responsible for proton translocation. V-ATPase activity leads to acidification of endosomes, phagosomes, lysosomes, secretory vesicles, and the trans-Golgi network, with extracellular acidification occurring in some specialized cells. Small molecule inhibitors of V-ATPase have played a crucial role in elucidating numerous aspects of cell biology by blocking acidification of intracellular compartments, while therapeutic use of V-ATPase inhibitors has been proposed for treatment of cancer, osteoporosis, and some infections. Here, we determine structures of the isolated VO complex from Saccharomyces cerevisiae bound to two well-known macrolide inhibitors: bafilomycin A1 and archazolid A. The structures reveal different binding sites for the inhibitors on the surface of the proton-carrying c ring, with only a small amount of overlap between the two sites. Binding of both inhibitors is mediated primarily through van der Waals interactions in shallow pockets and suggests that the inhibitors block rotation of the ring. Together, these structures indicate the existence of a large chemical space available for V-ATPase inhibitors that block acidification by binding the c ring.

biochemistry↗

bioRxiv2021

Coordinated conformational changes in the V1 complex during V-ATPase reversible dissociation

Vacuolar-type ATPases (V-ATPases) are rotary enzymes that acidify intracellular compartments in eukaryotic cells. These multi-subunit complexes consist of a cytoplasmic V1 region that hydrolyzes ATP and a membrane-embedded VO region that transports protons. V-ATPase activity is regulated by reversible dissociation of the two regions, with the isolated V1 and VO complexes becoming autoinhibited upon disassembly and subunit C subsequently detaching from V1. In yeast, assembly of the V1 and VO regions is mediated by the RAVE complex through an unknown mechanism. We used cryoEM of yeast V-ATPase to determine structures of the intact enzyme, the dissociated but complete V1 complex, and the V1 complex lacking subunit C. Upon separation, V1 undergoes a dramatic conformational rearrangement, with its rotational state becoming incompatible for reassembly with VO. Loss of subunit C allows V1 to match the rotational state of VO, suggesting how RAVE could reassemble V1 and VO by recruiting subunit C.

biochemistry↗

bioRxiv2021

Structure of mammalian V-ATPase with the TLDc domain protein mEAK7 bound

V-ATPases are rotary proton pumps that serve as signaling hubs with numerous proposed binding partners in cells. We used cryoEM combined with exhaustive focused classification to detect endogenous proteins that associate with V-ATPase from porcine kidney. A super-stoichiometric copy of subunit C was found in ~3% of complexes, while an additional ~1.6% of complexes bound mEAK-7, a protein with proposed roles in dauer formation in nematodes and mTOR signaling in mammals. High-resolution cryoEM of porcine kidney V-ATPase with recombinant mEAK-7 shows that mEAK-7s TLDc domain interacts with V-ATPases stator while its C-terminal helix binds V-ATPases rotor. This crosslink would be expected to inhibit rotary catalysis. However, unlike inhibition of yeast V-ATPase by the TLDc protein Oxr1p, exogenous mEAK-7 does not inhibit V-ATPase and mEAK-7 overexpression in cells does not alter lysosomal or phagosomal pH. Instead, cryoEM suggests that interaction of mEAK-7 with V-ATPase is disrupted by ATP-induced rotation of the rotor. Comparison of Oxr1p and mEAK-7 binding explains this difference. Together, these results show that differences in V-ATPase binding by TLDc domain-containing proteins can lead to effects ranging from strong inhibition to formation of labile interactions that are sensitive to the enzymes activity.

biochemistry↗

bioRxiv2021

Structural basis of Plasmodium vivax inhibition by antibodies binding to the circumsporozoite protein repeats

Malaria is a global health burden, with Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) responsible for the majority of infections worldwide. Circumsporozoite protein (CSP) is the most abundant protein on the surface of Plasmodium sporozoites, and antibodies targeting the central repeat region of CSP can prevent parasite infection. Although much has been uncovered about the molecular basis of antibody recognition of the PfCSP repeats, data remains scarce for PvCSP. Here, we performed molecular dynamics simulations for peptides comprising the PvCSP repeats from strains VK210 and VK247 to reveal how the PvCSP central repeats are highly disordered, with minor propensities to adopt turn conformations. Next, we solved eight crystal structures to unveil the interactions of two inhibitory monoclonal antibodies (mAbs), 2F2 and 2E10.E9, with PvCSP repeats. Both antibodies can accommodate subtle sequence variances in the repeat motifs and recognize largely coiled peptide conformations that also contain isolated turns. Our structural studies uncover various degrees of Fab-Fab homotypic interactions upon recognition of the PvCSP central repeats by these two inhibitory mAbs, similar to potent mAbs against PfCSP. These findings augment our understanding of host-Plasmodium interactions, and contribute molecular details of Pv inhibition by mAbs to unlock structure-based engineering of PvCSP-based vaccines.

molecular biology↗

bioRxiv2021

Detection and quantification of the vacuolar H ATPase using the Legionella effector protein SidK

Acidification of secretory and endocytic organelles is required for proper receptor recycling, membrane traffic, protein degradation, and solute transport. Proton-pumping vacuolar ATPases (V-ATPases) are responsible for this luminal acidification, which increases progressively as secretory and endocytic vesicles mature. An increasing density of V-ATPase complexes is thought to account for the gradual decrease in pH, but available reagents have not been sufficiently sensitive nor specific to test this hypothesis. We introduce a new probe to localize and quantify V-ATPases in eukaryotic cells. The probe is derived from SidK, a Legionella pneumophila effector protein that binds to the V-ATPase A subunit. We generated plasmids encoding fluorescent chimeras of SidK1-278, and labeled recombinant SidK1-278 with AlexaFluor-568 to visualize and quantify V-ATPases with high specificity in live and fixed cells, respectively. We show that V-ATPases are acquired progressively during phagosome maturation, that they distribute in discrete membrane subdomains, and that their density in lysosomes depends on the subcellular localization of the lysosome.

cell biology↗

bioRxiv2021

Structure of mycobacterial CIII2CIV2 respiratory supercomplex bound to the tuberculosis drug candidate telacebec (Q203)

The imidazopyridine telacebec, also known as Q203, is one of only a few new classes of compounds in more than fifty years with demonstrated antituberculosis activity in humans. Telacebec inhibits the mycobacterial respiratory supercomplex composed of complexes III and IV (CIII2CIV2). In mycobacterial electron transport chains, CIII2CIV2 replaces canonical CIII and CIV, transferring electrons from the intermediate carrier menaquinol to the final acceptor, molecular oxygen, while simultaneously transferring protons across the inner membrane to power ATP synthesis. We show that telacebec inhibits the menaquinol:oxygen oxidoreductase activity of purified Mycobacterium smegmatis CIII2CIV2 at concentrations similar to those needed to inhibit electron transfer in mycobacterial membranes and Mycobacterium tuberculosis growth in culture. We then used electron cryomicroscopy (cryoEM) to determine structures of CIII2CIV2 both in the presence and absence of telacebec. The structures suggest that telacebec prevents menaquinol oxidation by blocking two different menaquinol binding modes to prevent CIII2CIV2 activity.

biochemistry↗

bioRxiv2021

The respiratory supercomplex from C. glutamicum

Corynebacterium glutamicum is a preferentially aerobic Gram-positive bacterium belonging to the Actinobacteria phylum, which also includes the pathogen Mycobacterium tuberculosis. In the respiratory chain of these bacteria, complexes III (CIII) and IV (CIV) form a CIII2CIV2 supercomplex that catalyzes oxidation of menaquinol and reduction of dioxygen to water. Electron transfer within the CIII2CIV2 supercomplex is linked to transmembrane proton translocation, which maintains an electrochemical proton gradient that drives ATP synthesis and transport processes. We isolated the C. glutamicum supercomplex and used cryo-EM to determine its structure at 2.9 [A] resolution. The structure shows a central CIII2 dimer flanked by a CIV on each side. One menaquinone is bound in each of the QN and QP sites in each CIII, near the cytoplasmic and periplasmic sides, respectively. In addition, we identified a menaquinone positioned ~14 [A] from heme bL on the periplasmic side. A di-heme cyt. cc subunit provides an electronic connection between each CIII monomer and the adjacent CIV. In CIII2, the Rieske iron-sulfur (FeS) proteins are positioned with the iron near heme bL. Multiple subunits interact to form a convoluted sub-structure at the cytoplasmic side of the supercomplex, which defines a novel path that conducts protons into CIV.

biochemistry↗

bioRxiv2021

A Family of Glycosylated Macrolides Selectively Target Energetic Vulnerabilities in Leukemia

Cancer cells have long been recognized to exhibit unique bioenergetic requirements. The apoptolidin family of glycomacrolides are distinguished by their selective cytotoxicity towards oncogene transformed cells, yet their molecular mechanism remains uncertain. We used photoaffinity analogs of the apoptolidins to identify the F1 subcomplex of mitochondrial ATP synthase as the target of apoptolidin A. CryoEM of apoptolidin and ammocidin-ATP synthase complexes revealed a novel shared mode of inhibition that was confirmed by deep mutational scanning of the binding interface to reveal resistance mutations which were confirmed using CRISPR-Cas9. Ammocidin A was found to suppress leukemia progression in vivo at doses that were tolerated with minimal toxicity. The combination of cellular, structural, mutagenesis, and in vivo evidence define the mechanism of action of apoptolidin family glycomacrolides and establish a path to address OXPHOS-dependent cancers.

biochemistry↗

bioRxiv2021

Rieske head domain dynamics and indazole-derivative inhibition of Candida albicans complex III

During cellular respiration, electron transfer between the integral membrane protein complexes of the electron transport chain is coupled to proton translocation across the inner mitochondrial membrane, which in turn powers synthesis of ATP and transmembrane transport processes. The homodimeric electron transport chain Complex III (CIII2) oxidizes ubiquinol (UQH2) to ubiquinone (UQ), transferring electrons to cytochrome c, and translocating protons through a mechanism known as the Q cycle. The Q cycle involves UQH2 oxidation and UQ reduction at two different sites within each CIII monomer, as well as movement of the head domain of the Rieske subunit. We used cryoEM to determine the structure of CIII2 from Candida albicans, revealing density for endogenous UQ in the structure and allowing us to directly visualize the continuum of conformations of the Rieske head domain. Analysis of these conformations does not indicate cooperativity in the position of the Rieske head domains or binding of ligands in the two CIIIs of the CIII2 dimer. CryoEM with the indazole derivative Inz-5, which inhibits fungal CIII2 and is fungicidal when administered with fungistatic azole drugs, showed that inhibition by Inz-5 alters the equilibrium of the Rieske head domain positions.

biochemistry↗

bioRxiv2021

Structure of Ycf1p reveals the transmembrane domain TMD0 and the regulatory R region of ABCC transporters

ATP binding cassette (ABC) proteins typically function in active transport of solutes across membranes. The ABC core structure is comprised of two transmembrane domains (TMD1 and TMD2) and two cytosolic nucleotide binding domains (NBD1 and NBD2). Some members of the C-subfamily of ABC (ABCC) proteins, including human multidrug resistance proteins (MRPs), also possess an N-terminal transmembrane domain (TMD0) that contains five transmembrane -helices and is connected to the ABC core by the L0 linker. While TMD0 was resolved in SUR1, the atypical ABCC protein that is part of the hetero-octameric ATP-sensitive K+ channel, little is known about the structure of TMD0 in monomeric ABC transporters. Here, we present the structure of yeast cadmium factor 1 protein (Ycf1p), a homologue of human MRP1, determined by electron cryomicroscopy (cryo-EM). Comparison of Ycf1p, SUR1, and a structure of MRP1 that showed TMD0 at low resolution demonstrates that TMD0 can adopt different orientations relative to the ABC core, including a 145{degrees} rotation between Ycf1p and SUR1. The cryo-EM map also reveals that segments of the regulatory (R) region, which links NBD1 to TMD2 and was poorly resolved in earlier ABCC structures, interacts with the L0 linker, NBD1, and TMD2. These interactions, combined with fluorescence quenching experiments of isolated NBD1 with and without the R region, suggests how post-translational modifications of the R region modulate ABC protein activity. Mapping known mutations from MRP2 and MRP6 onto the Ycf1p structure explains how mutations involving TMD0 and the R region of these proteins lead to disease. Statement of SignificanceThe Ycf1p structure provides an atomic model for the TMD0 domain of ABCC transporters and for two segments of the regulatory (R) region that links NBD1 to TMD2. The orientation of TMD0 in Ycf1p differs from that seen in SUR1, the regulatory ABCC protein in KATP channels, demonstrating flexibility in TMD0/ABC core contacts. The structure suggests how post-translational modifications of the R region modulate ABC protein activity and provides a mechanistic understanding of several diseases that occur due to mutation of human homologues of Ycf1p.

biochemistry↗

bioRxiv2021

Polymeric assembly of endogenous Tuberous Sclerosis Protein Complex

Tuberous Sclerosis protein complex (pTSC) nucleates a proteinaceous signaling hub that integrates information about the internal and external energy status of the cell in regulation of growth and energy consumption. Biochemical and electron cryomicroscopy (cryoEM) studies of recombinant pTSC have revealed the structure and stoichiometry of the pTSC and have hinted at the possibility that the complex form large oligomers. Here, we have partially purified endogenous pTSC from fasted mammalian brains of rat and pig by leveraging a recombinant antigen binding fragment (Fab) specific for the TSC2 subunit of pTSC. We demonstrate Fab dependent purification of pTSC from membrane solubilized fractions of the brain homogenates. Negative stain electron microscopy of the samples purified from pig brain demonstrates rod-shaped protein particles with a width of 10 nm, a variable length as small as 40 nm and a high degree of conformational flexibility. Larger filaments are evident with a similar 10 nm width and up to 1 m in length in linear and web-like organizations prepared from pig brain. These observations suggest polymerization of endogenous pTSC into filamentous super-structures.

biochemistry↗

bioRxiv2020

Selective Targeting of Ras Mutant Cancers via a New Small Molecule

Mutations in the Ras family of oncogenes are implicated in 33% of human cancers, making Ras an intensely pursued target in drug discovery. As an alternative to direct pharmacological inhibition of Ras, we looked for sensitivities in RAS mutant cells. Using a small molecule screen in cell lines with mutations in Ras and its effector Raf, we discovered 249C as a Ras-mutant selective cytotoxic agent against a spectrum of RAS-mutant cancers. By combining CRISPR chemical-genetic screening, comparative profiling and chemoproteomics, we identified that 249C binds to a unique subunit on vacuolar (V)-ATPase with nanomolar affinity, inhibiting its biochemical activity and, unexpectedly, altering V-ATPase translocation in Ras-induced macropinocytosis. Via binding to V-ATPase, 249C prevents lysosomal acidification and inhibits autophagy and macropinocytosis pathways that several Ras-driven cancers rely on for survival. In characterizing 249Cs mechanism, we show that potency varies with the identity of the RAS driver mutation highlighting a mutant-specific dependence on autophagy and macropinocytosis. Indeed, 249C potently inhibits tumor growth without adverse side effects in a mouse xenograft model of KRAS-driven non-small cell lung cancer. These data establish proof-of-concept for targeting V-ATPase as a way to indirectly target specific Ras mutants, and provide a fundamental link between V-ATPase localization and specific Ras mutant tumor-related activity.

cancer biology↗