Complexin gains effective access to the assembling SNAREs via its membrane-binding C-terminal domain

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Complexin (Cpx) is a presynaptic protein essential for regulating synaptic vesicle (SV) fusion.
• Cpx's C-terminal domain (CTD) contains a membrane-binding motif critical for its function.
• The precise role of the CTD in Cpx's regulation of synaptic transmission beyond membrane targeting is not fully understood.

Purpose of the Study:

• To investigate the in vivo function of the Caenorhabditis elegans CPX-1 CTD in synaptic transmission.
• To determine if the CTD's role extends beyond membrane localization in regulating SV fusion.
• To elucidate the specific interactions required for CPX-1's inhibitory function on spontaneous SV fusion.

Main Methods:

• In vivo studies using Caenorhabditis elegans.
• Genetic manipulation of the CPX-1 C-terminal domain.
• Functional analysis of synaptic vesicle fusion and neurotransmission.

Main Results:

• The CPX-1 CTD significantly enhances the inhibition of spontaneous SV fusion.
• Replacing the CPX-1 CTD with the SV protein RAB-3 fully restored both fusogenic and inhibitory functions.
• Other SV proteins failed to restore CPX-1 function as efficiently as RAB-3, highlighting specificity.

Conclusions:

• Specific interaction of CPX-1 with the SV membrane via its CTD is essential for regulating spontaneous SV fusion.
• The CTD guides CPX-1 to sites of SNARE assembly, which are inaccessible from the cytoplasm.
• CPX-1's C-terminal membrane interactions are critical for its efficiency in controlling synaptic transmission.