Syntaxin 1A Transmembrane Domain Palmitoylation Induces a Fusogenic Conformation.

Area of Science:

• Molecular Biology
• Neuroscience
• Biophysics

Background:

• Neurotransmitter release relies on synaptic vesicle fusion, mediated by SNARE proteins like Synaptobrevin 2 (Syb2) and Syntaxin 1A (Stx1A).
• Palmitoylation, a post-translational modification, is known to affect protein function, but its role in SNARE transmembrane domain (TMD) mediated membrane fusion is unclear.

Purpose of the Study:

• To investigate the structural and functional consequences of SNARE TMD palmitoylation on synaptic vesicle fusion.
• To elucidate the mechanistic role of Stx1A and Syb2 palmitoylation in neurotransmitter release.

Main Methods:

• Coarse-grained molecular dynamics simulations using the MARTINI force field.
• Simulations of individual SNARE proteins, t-SNARE complexes, and fusion pore formation in lipid bilayers and nanodiscs.

Main Results:

• Stx1A palmitoylation reduces TMD tilting, stabilizing an upright SNARE domain conformation that facilitates SNARE complex formation.
• Stx1A palmitoylation delays fusion pore opening and reduces its flicker duration, while Syb2 palmitoylation has minimal impact on fusion pore dynamics.
• Dual palmitoylation of Stx1A and Syb2 modulates fusion pore duration and opening probability, indicating a complex regulatory role.

Conclusions:

• SNARE TMD palmitoylation plays a crucial role in multiple stages of neurotransmitter release, from priming to fusion pore dynamics.
• Stx1A palmitoylation facilitates early SNARE complex formation and directly impacts late-stage fusion pore events, promoting spontaneous release.