Synaptophysin controls synaptobrevin-II retrieval via a cryptic C-terminal interaction site.

Area of Science:

• Neuroscience
• Cell Biology
• Molecular Biology

Background:

• Synaptic vesicle (SV) protein retrieval during endocytosis is vital for neurotransmission.
• Synaptophysin (Syp) and synaptobrevin-II (SybII) are key SV proteins.
• Syp deficiency impairs SybII retrieval and slows SV endocytosis.

Purpose of the Study:

• To investigate the role of Syp's C-terminus in SV protein retrieval and endocytosis.
• To elucidate the mechanism by which Syp controls SybII retrieval.

Main Methods:

• Molecular replacement studies in primary cultures of Syp knockout neurons.
• Use of genetically encoded reporters for SV cargo trafficking.
• Analysis of SV endocytosis and SybII retrieval kinetics at physiological temperatures.

Main Results:

• SV endocytosis kinetics were not slowed in Syp knockout neurons at physiological temperatures.
• Neurons lacking Syp's C-terminus showed persistent defects in SybII retrieval.
• Sequential C-terminal truncations of Syp revealed a cryptic interaction site for SybII's SNARE motif.

Conclusions:

• Syp's sole presynaptic role is controlling SybII retrieval, not SV endocytosis kinetics.
• A conformational change in Syp's C-terminus is essential for SybII binding and accurate retrieval.
• This interaction is critical for maintaining neurotransmission efficiency.