Biology subjects

Howard, R. J.

Publications and source records attributed to Howard, R. J..

5 recordsLinked to original sources

bioRxiv2021

Markov state models of proton- and gate-dependent activation in a pentameric ligand-gated ion channel

Ligand-gated ion channels conduct currents in response to chemical stimuli, mediating electrochemical signaling in neurons and other excitable cells. For many channels the mechanistic details of gating remain unclear, partly due to limited structural data and simulation timescales. Here, we used enhanced sampling to simulate the pH-gated channel GLIC, and construct Markov state models (MSMs) of gating transitions. Consistent with new functional recordings reported here in oocytes, our analysis revealed differential effects of protonation and mutation on free-energy wells. Clustering of closed-versus open-like states enabled estimation of open probabilities and transition rates in each condition, while higher-order clustering affirmed conformational trends in gating. Furthermore, our models uncovered state- and protonation-dependent symmetrization among subunits. This demonstrates the applicability of MSMs to map energetic and conformational transitions between ion-channel functional states, and how they correctly reproduce shifts upon activation or mutation, with implications for modeling neuronal function and developing state-selective drugs.

biophysics↗

bioRxiv2021

Dynamic closed states of a ligand-gated ion channel captured by cryo-EM and simulations

Ligand-gated ion channels are critical mediators of electrochemical signal transduction across evolution. Biophysical and pharmacological characterization of these receptor proteins relies on high-quality structures in multiple, subtly distinct functional states. However, structural data in this family remain limited, particularly for resting and intermediate states on the activation pathway. Here we report cryo-electron microscopy (cryo-EM) structures of the proton-activated Gloeobacter violaceus ligand-gated ion channel (GLIC) under three pH conditions. Decreased pH was associated with improved resolution and sidechain rearrangements at the subunit/domain interface, particularly involving functionally important residues in the {beta}1-{beta}2 and M2-M3 loops. Molecular dynamics simulations substantiated flexibility in the closed-channel extracellular domains relative to the transmembrane ones, and supported electrostatic remodeling around E35 and E243 in proton-induced gating. Exploration of secondary cryo-EM classes further indicated a low-pH population with an expanded pore. These results support a dissection of protonation and activation steps in pH-stimulated conformational cycling in GLIC, including interfacial rearrangements largely conserved in the pentameric channel family.

biochemistry↗

bioRxiv2020

Assembly and symmetry of the fungal E3BP-containing core of the Pyruvate Dehydrogenase Complex

The pyruvate dehydrogenase complex (PDC) is a central component of all aerobic respiration, connecting glycolysis to mitochondrial oxidation of pyruvate. Despite its central metabolic role, its precise composition and means of regulation remain unknown. To explain the variation in stoichiometry reported for the E3-recruiting protein X (PX) in the fungal PDC, we established cryo-EM reconstructions of the native and recombinant PDC from the filamentous fungus and model organism Neurospora crassa. We find that the PX C-terminal domain localizes interior to the E2 core. Critically, we show that two distinct arrangements of a trimeric oligomer exists, which both result in strict tetrahedral symmetry of the PDC core interior. Both oligomerization and volume occlusion of the PDC interior by PX appears to limit its binding stoichiometry, which explains the variety of stoichiometries found previously for S. cerevisiae. This also suggests that the PX oligomer stability and size are potential mechanisms to dynamically adjust PDC compostion in response to external cues. Moreover, we find that the site where PX binds is conserved within fungi but not mammals, suggesting that it could be therapeutically targeted. To this end, we also show that a PX knockout results in loss of activity through dysfunctional E3 recruitment, leading to severely impaired N. crassa growth on sucrose. The fungal PDC is thus shown to be fundamentally similar to the mammalian PDC in function but subject to other conditions of possible regulation, conditioned by a steric restrictions imposed by the symmetry of the PDC and its components.

molecular biology↗

bioRxiv2020

Control of Cucumber green mottle mosaic virus in commercial greenhouse production with agricultural disinfectants and resistant cucumber varieties

Cucumber green mottle mosaic virus (CGMMV) is a re-emerging threat to greenhouse cucumber and other Cucurbitaceae crop productions worldwide. This seed-borne virus can easily spread from a contaminated seed to seedlings and to adjacent plants through mechanical contact of the foliage of diseased and healthy plants causing extensive yield losses. Additionally, infection may not be limited to the current crop but may also affect subsequent crops due to the long-term persistence of the virus on contaminated crop residues, greenhouse hard surfaces and soil or soil-less greenhouse substrates. In the present work, three greenhouse trials were conducted to develop an integrated pest management strategy towards controlling CGMMV in commercial cucumber greenhouses, by implementing an effective sanitization program and using resistant and grafted cucumber varieties. Results of sanitization trial highlighted that pressure washing and cleansing with an alkaline foam cleanser has eliminated CGMMV on some of the most heavily infested areas. However, three successive applications of cleanser and disinfectants were essential to completely eliminate CGMMV on porous and uneven surfaces, such as cement alleyway, tray gutter and floor mats. The varietal trial revealed that out of 15 cucumber varieties evaluated, two Mini ( Katrina and Khassib) and three Long English ( Sepire, Bomber and LC13900) had reduced or delayed CGMMV infection spread in the greenhouse but were intermediate in yield. The varieties Sunniwell and Bonbon were the most tolerant to CGMMV. They showed a high CGMMV infection level without compromising yield. These results proved the need for new productive cucumber varieties with CGMMV resistance. Grafting experiment showed only yield increase in case of grafted Picowell over Bonbon and not marked CGMMV resistance, which is a much desirable result when the grafting experiments are evaluated for their economic potential. In all, the current experimental trials unfold unique methodologies on CGMMV management in commercial greenhouses that are recommended to the growers to be followed for reducing crop losses and get benefitted on revenue compromise.

pathology↗

bioRxiv2020

Characterization of the dynamic resting state of a pentameric ligand-gated ion channel by cryo-electron microscopy and simulations

Ligand-gated ion channels are critical mediators of electrochemical signal transduction across evolution. Biophysical and pharmacological development in this family relies on high-quality structural data in multiple, subtly distinct functional states. However, structural data remain limited, particularly for the unliganded or resting state. Here we report cryo-electron microscopy structures of the Gloeobacter violaceus ligand-gated ion channel (GLIC) under resting and activating conditions (neutral and low pH). Parallel models were built either manually or using recently developed density-guided molecular simulations. The moderate resolution of resting-state reconstructions, particularly in the extracellular domain, was improved under activating conditions, enabling the visualization of residues at key subunit interfaces including loops B, C, F, and M2-M3. Combined with molecular dynamics simulations, the cryo-electron microscopy structures at different pH describe a heterogeneous population of closed channels, with activating conditions condensing the closed-channel energy landscape on a pathway towards gating.

biophysics↗