Synapsin I: a regulated synaptic vesicle organizing protein.

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Synapsin is a nerve terminal protein associated with synaptic vesicles.
• It shares homology with erythrocyte protein 4.1 and spectrin.
• Synapsin is a substrate for cyclic AMP and Ca/calmodulin-dependent protein kinases.

Purpose of the Study:

• To characterize the structural and functional properties of synapsin.
• To investigate synapsin's role in interconnecting synaptic vesicles with cellular components.
• To explore the physiological function of synapsin in neuronal signaling.

Main Methods:

• In vitro binding assays to determine affinities (Kd) for synaptic vesicles, membranes, spectrin, microtubules, and neurofilaments.
• Phosphorylation assays using Ca/calmodulin-dependent protein kinase.

Main Results:

• Synapsin binds synaptic vesicles and membranes with high affinity (Kd 0.01-0.02 microM).
• Synapsin associates with spectrin, microtubules, and neurofilaments in vitro (Kd 0.5-4 microM).
• Phosphorylation by Ca/calmodulin-dependent protein kinase inhibits synapsin's ability to interconnect vesicles and membranes.

Conclusions:

• Synapsin functions as a structural protein in neurons, linking synaptic vesicles to membranes and cytoskeletal elements.
• Its activity is regulated by phosphorylation, suggesting a role in calcium-mediated signaling.
• Synapsin may organize vesicles during axonal transport and anchor them at active zones.