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Published 26 September 2005. doi:10.1083/jcb.200504055
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 170, Number 7, 1113-1125
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Article

 PKA-catalyzed phosphorylation of tomosyn and its implication in Ca2+-dependent exocytosis of neurotransmitter

Takeshi Baba1, Toshiaki Sakisaka1, Sumiko Mochida2, and Yoshimi Takai1

1 Department of Molecular Biology and Biochemistry, Osaka University Graduate School of Medicine/Faculty of Medicine, Suita 565-0871, Japan
2 Department of Physiology, Tokyo Medical University, Shinjuku 160-8402, Japan

Correspondence to Yoshimi Takai: ytakai{at}molbio.med.osaka-u.ac.jp

Neurotransmitter is released from nerve terminals by Ca2+-dependent exocytosis through many steps. SNARE proteins are key components at the priming and fusion steps, and the priming step is modulated by cAMP-dependent protein kinase (PKA), which causes synaptic plasticity. We show that the SNARE regulatory protein tomosyn is directly phosphorylated by PKA, which reduces its interaction with syntaxin-1 (a component of SNAREs) and enhances the formation of the SNARE complex. Electrophysiological studies using cultured superior cervical ganglion (SCG) neurons revealed that this enhanced formation of the SNARE complex by the PKA-catalyzed phosphorylation of tomosyn increased the fusion-competent readily releasable pool of synaptic vesicles and, thereby, enhanced neurotransmitter release. This mechanism was indeed involved in the facilitation of neurotransmitter release that was induced by a potent biological mediator, the pituitary adenylate cyclase-activating polypeptide, in SCG neurons. We describe the roles and modes of action of PKA and tomosyn in Ca2+-dependent neurotransmitter release.

Abbreviations used in this paper: CBB, Coomassie brilliant blue; EPSP, excitatory postsynaptic potential; Lgl, lethal giant larvae; MBP, maltose-binding protein; PACAP, pituitary adenylate cyclase-activating polypeptide; PKI, protein kinase peptide inhibitor; ROCK, Rho-associated coiled-coil–forming kinase; RRP, readily releasable pool; SCG, superior cervical ganglion; siRNA, small interference RNA; SRP, slowly releasable pool; VAMP, vesicle-associated membrane protein.


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