Membrane Binding of α-Synuclein Stimulates Expansion of SNARE-Dependent Fusion Pore.

Ryan Khounlo,Nam Ki Lee,Brenden J D Hawk,Josh Pierson,Yeon-Kyun Shin,Tung-Mei Khu,Gyeongji Yoo

doi:10.3389/fcell.2021.663431

Abstract

SNARE-dependent membrane fusion is essential for neurotransmitter release at the synapse. Recently, α-synuclein has emerged as an important regulator for membrane fusion. Misfolded α-synuclein oligomers are potent fusion inhibitors. However, the function of normal α-synuclein has been elusive. Here, we use the single vesicle-to-supported bilayer fusion assay to dissect the role of α-synuclein in membrane fusion. The assay employs 10 kD Rhodamine B-dextran as the content probe that can detect fusion pores larger than ∼6 nm. We find that the SNARE complex alone is inefficient at dilating fusion pores. However, α-synuclein dramatically increases the probability as well as the duration of large pores. When the SNARE-interacting C-terminal region of α-synuclein was truncated, the mutant behaves the same as the wild-type. However, the double proline mutants compromising membrane-binding show significantly reduced effects on fusion pore expansion. Thus, our results suggest that α-synuclein stimulates fusion pore expansion specifically through its membrane binding.

Highlights

Communication between neurons, which underlies cognition, memory, and motor movement, is built upon neurotransmitter release at the synapse
We find that the SNARE complex alone is inefficient at dilating fusion pores
Membrane Binding of αS Plays a Role in Stimulating Fusion Pore Expansion

Summary

Introduction

Communication between neurons, which underlies cognition, memory, and motor movement, is built upon neurotransmitter release at the synapse. Cargo vesicles undergo membrane fusion with the plasma membrane, which releases the neurotransmitters into the synaptic cleft. It is established that the widely conserved SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptor) complex is the minimal machinery that drives membrane fusion (Sollner et al, 1993; Weber et al, 1998). SNARE motifs from vesicle-associated v-SNARE VAMP2 (or synaptobrevin 2) and those from target plasma membrane t-SNAREs, syntaxin-1A and SNAP-25, form a highly stable parallel coiled-coil (Poirier et al, 1998; Sutton et al, 1998). Hemifusion, in which outer leaflets of two bilayers are merged but inner leaflets are not

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Conclusion