Biology subjects

Maksaev, G.

Publications and source records attributed to Maksaev, G..

4 recordsLinked to original sources

bioRxiv2022

OzTracs: Optical Osmolality Reporters Engineered from Mechanosensitive Ion Channels

Interactions between physical forces and membrane proteins underpin many forms of environmental sensation and acclimation. Microbes survive sudden osmotic stresses with the help of mechanically gated ion channels and osmolyte transporters. Plant mechanosensitive ion channels have been shown to function in defense signaling. Here, we engineered genetically encoded osmolality sensors (OzTracs) by fusing green fluorescent protein spectral variants to the mechanosensitive ion channels MscL from E. coli or MSL10 from A. thaliana. When expressed in yeast cells, OzTrac sensors reported osmolality changes as a proportional change in emission ratio of the two fluorescent protein domains. Live-cell imaging revealed accumulation of fluorescent sensors in internal aggregates presumably derived from the endomembrane system. Thus, OzTrac sensors serve as osmolality-dependent reporters through an indirect mechanism, such as effects on molecular crowding or fluorophore solvation.

cell biology↗

bioRxiv2020

Cryo-EM structures of the ATP release channel pannexin 1

The plasma membrane ATP release channel pannexin 1 has been implicated in numerous physiological and pathophysiological processes associated with purinergic signaling, including cancer progression, apoptotic cell clearance, inflammation, blood pressure regulation, oocyte development, epilepsy and neuropathic pain. Here, we present near-atomic resolution structures of Xenopus tropicalis and Homo sapiens PANX1 determined by cryo-electron microscopy that reveal a heptameric channel architecture. Compatible with ATP permeation, the transmembrane pore and cytoplasmic vestibule are exceptionally wide. An extracellular tryptophan ring located at the outer pore creates a constriction site, potentially functioning as a molecular sieve that restricts the size of permeable substrates. In combination with functional characterization, this work elucidates the previously unknown architecture of pannexin channels and establishes a foundation for understanding their unique channel properties as well as for developing rational therapies.

biophysics↗

bioRxiv2019

Atomistic basis of opening and conduction in mammalian inward rectifier potassium (Kir2.2) channels

Potassium ion conduction through open potassium channels is essential to control of membrane potentials in all cells. To elucidate the open conformation and hence the mechanism of K+ ion conduction in the classical inward rectifier Kir2.2, we introduced a negative charge (G178D) at the crossing point of the inner helix bundle (HBC), the location of ligand-dependent gating. This forced open mutation generated channels that were active even in the complete absence of phosphoinositol-4,5-bisphosphate (PIP2), an otherwise essential ligand for Kir channel opening. Crystal structures were obtained at a resolution of 3.6 [A] without PIP2 bound, or 2.8 [A] in complex with PIP2. The latter revealed a slight widening at the HBC, through backbone movement. Molecular dynamics (MD) simulations showed that subsequent spontaneous wetting of the pore through the HBC gate region allowed K+ ion movement across the HBC and conduction through the channel. Further simulations reveal atomistic details of the opening process and highlight the role of pore lining acidic residues in K+ conduction through Kir2 channels.

biophysics↗

bioRxiv2018

Nonpolar Residues in the Presumptive Pore-Lining Helix of Mechanosensitive Channel MSL10 Influence Channel Behavior and Confirm a Non-Conducting Function

Mechanosensitive (MS) ion channels provide a universal mechanism for sensing and responding to increased membrane tension. MscS-Like(MSL)10 is a relatively well-studied MS ion channel from Arabidopsis thaliana that is implicated in cell death signaling. The relationship between the amino acid sequence of MSL10 and its conductance, gating tension, and opening and closing kinetics remain unstudied. Here we identify several nonpolar residues in the presumptive pore-lining transmembrane helix of MSL10 (TM6) that contribute to these basic channel properties. F553 and I554 are essential for wild type channel conductance and the stability of the open state. G556, a glycine residue located at a predicted kink in TM6, is essential for channel conductance. The increased tension sensitivity of MSL10 compared to close homolog MSL8 may be attributed to F563, but other channel characteristics appear to be dictated by more global differences in structure. Finally, MSL10 F553V and MSL10 G556V provided the necessary tools to establish that MSL10s ability to trigger cell death is independent of its ion channel function.

plant biology↗