Homo- and heterodimerization of synapsins

Area of Science:

• Neuroscience
• Molecular Biology
• Protein Biochemistry

Background:

• Synapsins are a family of synaptic vesicle proteins in vertebrates, encoded by three genes.
• They possess a conserved, ATP-binding C-domain, crucial for their function.
• Previous studies revealed the C-domain of synapsin I forms stable dimers.

Purpose of the Study:

• To investigate the dimerization properties of all synapsin C-domains.
• To determine if synapsins form homo- and heterodimers.
• To understand the in vivo implications of synapsin interactions.

Main Methods:

• Yeast two-hybrid screens to identify interacting synapsin domains.
• Quantitative yeast two-hybrid assays for protein-protein binding strength.
• Immunoprecipitation from transfected cells and bacterial expression systems.
• Analysis of synapsin III levels in synapsin I/II double knockout mice.

Main Results:

• Yeast two-hybrid screens identified synapsin C-domains as strong interaction partners.
• Quantitative assays confirmed robust pairwise interactions among all synapsins.
• Immunoprecipitation demonstrated synapsin II heteromultimerization with synapsins I and III in cells and bacteria.
• Synapsin III levels were reduced by 50% in synapsin I/II double knockout mice, indicating in vivo heteromerization and stabilization.

Conclusions:

• All synapsin C-domains form homodimers and heterodimers.
• These homo- and heterodimers likely coat synaptic vesicles.
• In vivo heteromultimerization of synapsins is essential for protein stabilization, with synapsin III not compensating for the loss of synapsins I and II.