Effects of synaptic vesicles on actin polymerization.
We have analyzed the effects of synaptic vesicles on actin polymerization by using a time-resolved spectrofluorometric assay. We have found that synaptic vesicles have complex effects on the kinetics of actin polymerization, which vary depending on whether the synaptic vesicle-specific phosphoprotein synapsin I is absent or present on their membrane. Synapsin I bound either to synaptic vesicles or to pure phospholipid vesicles exhibits phosphorylation-dependent actin-nucleating activity. Synaptic vesicles depleted of endogenous synapsin I decrease the rate and the final extent of actin polymerization, an effect which is not observed with pure phospholipid vesicles. Thus, the state of association of synapsin I with synaptic vesicles, which is modulated by its state of phosphorylation, may affect actin assembly and the physico-chemical characteristics of the synaptic vesicle microenvironment.
Chieregatti
E
E
Dept. of Medical Pharmacology, University of Milan, Italy.
Ceccaldi
P E
PE
Benfenati
F
F
Valtorta
F
F
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D007700:Kinetics; D008567:Membranes, Artificial; D009994:Osmolar Concentration; D010766:Phosphorylation; D011108:Polymers; D051381:Rats; D013050:Spectrometry, Fluorescence; D016704:Synapsins / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000737:chemistry / Q000378:metabolism*; D014783:Viscosity
D000199:Actins; D008567:Membranes, Artificial; D011108:Polymers; D016704:Synapsins