Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Sheenah Bryant is active.

Publication


Featured researches published by Sheenah Bryant.


Purinergic Signalling | 2016

Purinergic control of lysenin’s transport and voltage-gating properties

Sheenah Bryant; Nisha Shrestha; Paul Carnig; Samuel Kosydar; Philip Belzeski; Charles B. Hanna; Daniel Fologea

Lysenin, a pore-forming protein extracted from the coelomic fluid of the earthworm Eisenia foetida, manifests cytolytic activity by inserting large conductance pores in host membranes containing sphingomyelin. In the present study, we found that adenosine phosphates control the biological activity of lysenin channels inserted into planar lipid membranes with respect to their macroscopic conductance and voltage-induced gating. Addition of ATP, ADP, or AMP decreased the macroscopic conductance of lysenin channels in a concentration-dependent manner, with ATP being the most potent inhibitor and AMP the least. ATP removal from the bulk solutions by buffer exchange quickly reinstated the macroscopic conductance and demonstrated reversibility. Single-channel experiments pointed to an inhibition mechanism that most probably relies on electrostatic binding and partial occlusion of the channel-conducting pathway, rather than ligand gating induced by the highly charged phosphates. The Hill analysis of the changes in macroscopic conduction as a function of the inhibitor concentration suggested cooperative binding as descriptive of the inhibition process. Ionic screening significantly reduced the ATP inhibitory efficacy, in support of the electrostatic binding hypothesis. In addition to conductance modulation, purinergic control over the biological activity of lysenin channels has also been observed to manifest as changes of the voltage-induced gating profile. Our analysis strongly suggests that not only the inhibitor’s charge but also its ability to adopt a folded conformation may explain the differences in the observed influence of ATP, ADP, and AMP on lysenin’s biological activity.


European Biophysics Journal | 2016

Intramembrane congestion effects on lysenin channel voltage-induced gating

Eric Krueger; Sheenah Bryant; Nisha Shrestha; Tyler Clark; Charles B. Hanna; David A. Pink; Daniel Fologea

All cell membranes are packed with proteins. The ability to investigate the regulatory mechanisms of protein channels in experimental conditions mimicking their congested native environment is crucial for understanding the environmental physicochemical cues that may fundamentally contribute to their functionality in natural membranes. Here we report on investigations of the voltage-induced gating of lysenin channels in congested conditions experimentally achieved by increasing the number of channels inserted into planar lipid membranes. Typical electrophysiology measurements reveal congestion-induced changes to the voltage-induced gating, manifested as a significant reduction of the response to external voltage stimuli. Furthermore, we demonstrate a similar diminished voltage sensitivity for smaller populations of channels by reducing the amount of sphingomyelin in the membrane. Given lysenin’s preference for targeting lipid rafts, this result indicates the potential role of the heterogeneous organization of the membrane in modulating channel functionality. Our work indicates that local congestion within membranes may alter the energy landscape and the kinetics of conformational changes of lysenin channels in response to voltage stimuli. This level of understanding may be extended to better characterize the role of the specific membrane environment in modulating the biological functionality of protein channels in health and disease.


The Scientific World Journal | 2013

Cationic Polymers Inhibit the Conductance of Lysenin Channels

Daniel Fologea; Eric Krueger; Steve Rossland; Sheenah Bryant; Tyler Clark

The pore-forming toxin lysenin self-assembles large and stable conductance channels in natural and artificial lipid membranes. The lysenin channels exhibit unique regulation capabilities, which open unexplored possibilities to control the transport of ions and molecules through artificial and natural lipid membranes. Our investigations demonstrate that the positively charged polymers polyethyleneimine and chitosan inhibit the conducting properties of lysenin channels inserted into planar lipid membranes. The preservation of the inhibitory effect following addition of charged polymers on either side of the supporting membrane suggests the presence of multiple binding sites within the channels structure and a multistep inhibition mechanism that involves binding and trapping. Complete blockage of the binding sites with divalent cations prevents further inhibition in conductance induced by the addition of cationic polymers and supports the hypothesis that the binding sites are identical for both multivalent metal cations and charged polymers. The investigation at the single-channel level has shown distinct complete blockages of each of the inserted channels. These findings reveal key structural characteristics which may provide insight into lysenins functionality while opening innovative approaches for the development of applications such as transient cell permeabilization and advanced drug delivery systems.


Scientific Reports | 2017

Stochastic sensing of Angiotensin II with lysenin channels

Nisha Shrestha; Sheenah Bryant; Christopher Thomas; Devon Richtsmeier; Xinzhu Pu; Juliette K. Tinker; Daniel Fologea

The ability of pore-forming proteins to interact with various analytes has found vast applicability in single molecule sensing and characterization. In spite of their abundance in organisms from all kingdoms of life, only a few pore-forming proteins have been successfully reconstituted in artificial membrane systems for sensing purposes. Lysenin, a pore-forming toxin extracted from the earthworm E. fetida, inserts large conductance nanopores in lipid membranes containing sphingomyelin. Here we show that single lysenin channels may function as stochastic nanosensors by allowing the short cationic peptide angiotensin II to be electrophoretically driven through the conducting pathway. Long-term translocation experiments performed using large populations of lysenin channels allowed unequivocal identification of the unmodified analyte by Liquid Chromatography-Mass Spectrometry. However, application of reverse voltages or irreversible blockage of the macroscopic conductance of lysenin channels by chitosan addition prevented analyte translocation. This investigation demonstrates that lysenin channels have the potential to function as nano-sensing devices capable of single peptide molecule identification and characterization, which may be further extended to other macromolecular analytes.


Journal of Nanobiotechnology | 2017

ZnO nanoparticles modulate the ionic transport and voltage regulation of lysenin nanochannels

Sheenah Bryant; Josh Eixenberger; Steven Rossland; Holly Apsley; Connor Hoffmann; Nisha Shrestha; Michael McHugh; Alex Punnoose; Daniel Fologea

BackgroundThe insufficient understanding of unintended biological impacts from nanomaterials (NMs) represents a serious impediment to their use for scientific, technological, and medical applications. While previous studies have focused on understanding nanotoxicity effects mostly resulting from cellular internalization, recent work indicates that NMs may interfere with transmembrane transport mechanisms, hence enabling contributions to nanotoxicity by affecting key biological activities dependent on transmembrane transport. In this line of inquiry, we investigated the effects of charged nanoparticles (NPs) on the transport properties of lysenin, a pore-forming toxin that shares fundamental features with ion channels such as regulation and high transport rate.ResultsThe macroscopic conductance of lysenin channels greatly diminished in the presence of cationic ZnO NPs. The inhibitory effects were asymmetrical relative to the direction of the electric field and addition site, suggesting electrostatic interactions between ZnO NPs and a binding site. Similar changes in the macroscopic conductance were observed when lysenin channels were reconstituted in neutral lipid membranes, implicating protein-NP interactions as the major contributor to the reduced transport capabilities. In contrast, no inhibitory effects were observed in the presence of anionic SnO2 NPs. Additionally, we demonstrate that inhibition of ion transport is not due to the dissolution of ZnO NPs and subsequent interactions of zinc ions with lysenin channels.ConclusionWe conclude that electrostatic interactions between positively charged ZnO NPs and negative charges within the lysenin channels are responsible for the inhibitory effects on the transport of ions. These interactions point to a potential mechanism of cytotoxicity, which may not require NP internalization.


Toxins | 2018

Insights into the Voltage Regulation Mechanism of the Pore-Forming Toxin Lysenin

Sheenah Bryant; Tyler Clark; Christopher Thomas; Kaitlyn Ware; Andrew Bogard; Colleen Calzacorta; Daniel Prather; Daniel Fologea

Lysenin, a pore forming toxin (PFT) extracted from Eisenia fetida, inserts voltage-regulated channels into artificial lipid membranes containing sphingomyelin. The voltage-induced gating leads to a strong static hysteresis in conductance, which endows lysenin with molecular memory capabilities. To explain this history-dependent behavior, we hypothesized a gating mechanism that implies the movement of a voltage domain sensor from an aqueous environment into the hydrophobic core of the membrane under the influence of an external electric field. In this work, we employed electrophysiology approaches to investigate the effects of ionic screening elicited by metal cations on the voltage-induced gating and hysteresis in conductance of lysenin channels exposed to oscillatory voltage stimuli. Our experimental data show that screening of the voltage sensor domain strongly affects the voltage regulation only during inactivation (channel closing). In contrast, channel reactivation (reopening) presents a more stable, almost invariant voltage dependency. Additionally, in the presence of anionic Adenosine 5′-triphosphate (ATP), which binds at a different site in the channel’s structure and occludes the conducting pathway, both inactivation and reactivation pathways are significantly affected. Therefore, the movement of the voltage domain sensor into a physically different environment that precludes electrostatically bound ions may be an integral part of the gating mechanism.


Archive | 2018

Modulation of Membrane Transport via Lysenin Channels Controlled by Electrochemical Gradients

Philip Belzeski; Nisha Shrestha; Daniel Prather; Samuel Kosydar; Sheenah Bryant


Biophysical Journal | 2018

Mechanical Stress Modulates Cytosolic Ca2+ in MLO-Y4 Osteocyte-Like Cells

Sheenah Bryant; Elizabeth T. Leung; Daniel Prather; Conner Patricelli; Daniel Fologea


Biophysical Journal | 2018

Control of Membrane Permeability via Voltage Regulated Lysenin Channels

Philip Belzeski; Sheenah Bryant; Nisha Shrestha; Daniel Prather; Samuel Kosydar; Daniel Fologea


Biophysical Journal | 2018

ATP and AMP Reshape the Energy Landscape of Voltage-Gated Lysenin Channels in a Charge and Concentration Dependent Manner

Daniel Prather; Sheenah Bryant; Nisha Shrestha; K. Summer Ware; Andy Bogard; Philip Belzeski; Daniel Fologea

Collaboration


Dive into the Sheenah Bryant's collaboration.

Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Paul Carnig

Boise State University

View shared research outputs
Researchain Logo
Decentralizing Knowledge