Fluorescence approaches to the study of the actin-nucleating and bundling activities of synapsin I.
Synapsin I is a neuron-specific phosphoprotein which binds to small synaptic vesicles and actin in a phosphorylation-dependent fashion. We have analyzed the ability of synapsin I to interact with actin monomers and filaments using purified proteins derivatized with fluorescent probes. Synapsin I accelerates the initial rate of actin polymerization and increases the final steady-state levels of polymerized actin. The fraction of total actin polymerized by synapsin I strongly depends on the synapsin I-actin ratio. We have visualized the actin-bundling activity of synapsin I using a non-perturbing method, video-enhanced microscopy of fluoresceinated synapsin I and actin filaments. Our findings suggest that synapsin I exerts a control on the physical characteristics of the cytoskeletal network of the nerve terminal and are consistent with the proposed role of synapsin I in mediating the interaction of synaptic vesicles with actin.
Valtorta
F
F
B Ceccarelli Center, Department of Pharmacology, University of Milan, Italy.
Ceccaldi
P E
PE
Grohovaz
F
F
Chieregatti
E
E
Fesce
R
R
Benfenati
F
F
D000199:Actins / Q000502:physiology*; D000818:Animals; D002417:Cattle; D019793:Fluorescein; D005452:Fluoresceins; D005470:Fluorometry; D008853:Microscopy / Q000379:methods; D011108:Polymers / Q000378:metabolism; D016704:Synapsins / Q000502:physiology*; D013690:Television
D000199:Actins; D005452:Fluoresceins; D011108:Polymers; D016704:Synapsins; D019793:Fluorescein