Voltage‐activated complexation of α‐synuclein with three diverse β‐barrel channels: VDAC, MspA, and α‐hemolysin

Abstract

Voltage-activated complexation is the process by which a transmembrane potential drives complex formation between a membrane-embedded channel and a soluble or membrane-peripheral target protein. Metabolite and calcium flux across the mitochondrial outer membrane was shown to be regulated by voltage-activated complexation of the voltage-dependent anion channel (VDAC) and either dimeric tubulin or αsynuclein (αSyn). However, the roles played by VDAC's characteristic attributes-its anion selectivity and voltage gating behavior-have remained unclear. Here, we compare in vitro measurements of voltage-activated complexation of αSyn with three wellcharacterized β-barrel channels-VDAC, MspA, and α-hemolysin-that differ widely in their organism of origin, structure, geometry, charge density distribution, and voltage gating behavior. The voltage dependences of the complexation dynamics for the different channels are observed to differ quantitatively but have similar qualitative features. In each case, energy landscape modeling describes the complexation dynamics in a manner consistent with the known properties of the individual channels, while voltage gating does not appear to play a role. The reaction free energy landscapes thus calculated reveal a non-trivial dependence of the αSyn/channel complex stability on the surface density of αSyn.

Blocker Effect on Diffusion Resistance of a Membrane Channel: Dependence on the Blocker Geometry

“…where R acc is the access resistance given in eq 1. 7, and R ws is the intrinsic diffusion resistance of the channel with the blocking cylinder given by…”

“…It is emerging as a powerful tool for detection and analysis of analytes of diverse origin at a single molecule level. A substantial progress has already been achieved in DNA and protein sequencing, − investigations of protein-protein interactions, , and studies in single-molecule enzymology and post-translational protein modifications. − Nanopore sensing is based on the fact that upon their passage through a nanopore different analyte molecules reduce, that is, partially block, the nanopore current to a different extent, thus allowing to gauge their physico-chemical properties. Though there is a well-appreciated progress in quantitative understanding of the amplitude and time characteristics of the analyte-induced transients in nanopore current, − a reliable theoretical background of this phenomenon is still missing.…”

Highlights on the current state of proteomic detection and characterization with nanopore sensors

“…Many studies have modelled polymers in the nanopore environment as they interact with a collection of free energy barriers to transport (i.e., capture, partitioning, and escape) [9–13] and this can help researchers better understand optimization strategies for designing better sensors. Hoogerheide and colleagues [14] extend this theme with a study on voltage dependent transport of α‐synuclein and a variety of nanochannels. This study models the free energy profile of the α‐synuclein peptides, which yields numerous conclusions about the nature of the polymer–pore interactions.…”

Trapping of single diffusing particles by a circular disk on a reflecting flat surface. Absorbing hemisphere approximation

“…17 It was shown that in this signaling mechanism the disordered tail is trapped by the channel whereas the rest of the protein body – its structured part – serves as a membrane-bound anchor. 18…”

“…17 It was shown that in this signaling mechanism the disordered tail is trapped by the channel whereas the rest of the protein body -its structured part -serves as a membranebound anchor. 18 In developing the theory, two questions naturally arise: (1) how to choose the hemisphere radius and ( 2) what is the range of applicability of our approach that ignores the angular dependence? Our choice of the hemisphere radius is discussed in the next Section 2.…”