Biology subjects

Reichow, S. L.

Publications and source records attributed to Reichow, S. L..

3 recordsLinked to original sources

bioRxiv2020

Connexin 46 and connexin 50 gap junction channel open stability and unitary conductance are shaped by structural and dynamic features of their N-terminal domains

The connexins form intercellular communication channels, known as gap junctions (GJs), that facilitate diverse physiological roles in vertebrate species, ranging from electrical coupling and long-range chemical signaling, to coordinating development and nutrient exchange. GJs formed by different connexins are expressed throughout the body and harbor unique channel properties that have not been fully defined mechanistically. Recent structural studies have implicated the amino-terminal (NT) domain as contributing to isoform-specific functional differences that exist between the lens connexins, Cx50 and Cx46. To better understand the structural and functional differences in the two closely related, yet functionally distinct GJs, we constructed models corresponding to CryoEM-based structures of the wildtype Cx50 and Cx46 GJs, NT domain swapped chimeras (Cx46-50NT and Cx50-46NT), and point variants at the 9th residue (Cx46-R9N and Cx50-N9R) for comparative MD simulation and electrophysiology studies. All of these constructs formed functional GJ channels, except Cx46-50NT, which correlated with increased dynamical behavior (instability) of the NT domain observed by MD simulation. Single channel conductance (γj) also correlated well with free-energy landscapes predicted by MD, where γj of Cx46-R9N was increased from Cx46 and the γjs of Cx50-46NT and Cx50-N9R was decreased from Cx50, but to a surprisingly greater degree. Additionally, we observed significant effects on transjunctional voltage-dependent gating (Vj-gating) and open-state dwell times induced by the designed NT domain variants. Together, these studies indicate that the NT domains of Cx46 and Cx50 play an important role in defining channel properties related to open-state stability and single channel conductance.Competing Interest StatementThe authors have declared no competing interest.AbbreviationsGJgap junctionGjgap junctional coupling conductanceγjsingle gap junction channel conductanceIjmacroscopic transjunctional currentijsingle gap junction channel currentCx46sheep connexin 46Cx50sheep connexin 50Vjtransjunctional voltageMDmolecular dynamicsr.m.s.d.root mean square deviationr.m.s.f.root mean square fluctuationPMFpotential of mean forceView Full Text

biophysics↗

bioRxiv2020

Automated and statistically corrected identification of flexible multivalent IDP-bound assemblies in electron micrographs

Multivalent intrinsically disordered protein (IDP) complexes are prevalent in biology and control diverse cellular functions, including tuning levels of transcription, coordinating cell-signaling events, and regulating the assembly and disassembly of complex macromolecular architectures. These systems pose a significant challenge to structural investigation, due to the continuum dynamics imparted by the IDP and compositional heterogeneity resulting from characteristic low-affinity interactions. Traditional single-particle electron microscopy (EM) is a powerful tool for visualizing IDP complexes. However, the IDPs themselves are typically "invisible" by EM, undermining methods of image analysis and structural interpretation. To overcome these challenges, we developed a pipeline for automated analysis of common beads-on-a-string type of assemblies, composed of IDPs bound at multivalent sites to the ubiquitous ~20 kDa cross-linking hub protein LC8. This approach quantifies conformational and compositional heterogeneity on a single-particle basis, and statistically corrects spurious observations arising from random proximity of bound and unbound LC8. After careful validation of the methodology, the approach was applied to the nuclear pore IDP Nup159 and the transcription factor ASCIZ. The analysis unveiled significant compositional and conformational diversity in both systems that could not be obtained from traditional single particle EM class-averaging strategies, and shed new light on how these architectural properties contribute to their physiological roles in supramolecular assembly and transcriptional regulation. Ultimately, we expect that this approach may be adopted to many other intrinsically disordered systems that have evaded traditional methods of structural characterization. Significance StatementIntrinsically disordered proteins (IDPs) or protein regions (IDRs) represent >30% of the human proteome, but mechanistically remain some of the most poorly understood classes of proteins in biology. This dearth in understanding stems from these very same intrinsic and dynamic properties, which make them difficult targets for quantitative and structural characterization. Here, we present an automated approach for extracting quantitative descriptions of conformational and compositional heterogeneity present in a common beads-on-a-string type of multivalent IDP system from single-particle images in electron micrographs. This promising approach may be adopted to many other intrinsically disordered systems that have evaded traditional ensemble methods of characterization.

biophysics↗

bioRxiv2020

Connexin-46/50 in a dynamic lipid environment resolved by CryoEM at 1.9 A

Gap junctions establish direct pathways for connected cells and tissues to transfer metabolic and electrical messages1. The local lipid environment is known to affect the structure, stability and intercellular channel activity of gap junctions2-5; however, the molecular basis for these effects remains unknown. To gain insight toward how gap junctions interact with their local membrane environment, we used lipid nanodisc technology to incorporate native connexin-46/50 (Cx46/50) intercellular channels into a dual lipid membrane system, closely mimicking a native cell-to-cell junction. Structural characterization of Cx46/50 lipid-embedded channels by single particle CryoEM revealed a lipid-induced stabilization to the channel, resulting in a 3D reconstruction at 1.9 [A] resolution. Together with all-atom molecular dynamics (MD) simulations and 3D heterogeneity analysis of the ensemble CryoEM data, it is shown that Cx46/50 in turn imparts long-range stabilization to the dynamic local lipid environment that is specific to the extracellular lipid leaflet of the two opposed membranes. In addition, nearly 400 water molecules are resolved in the CryoEM map, localized throughout the intercellular permeation pathway and contributing to the channel architecture. These results illustrate how the aqueous-lipid environment is integrated with the architectural stability, structure and function of gap junction communication channels, and demonstrates the ability of CryoEM to effectively characterize dynamical protein-lipid interactions.

biophysics↗