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JCS ePress
online publication date 3 Jun 2003
doi: 10.1242/jcs.00595
Research Article
Molecular determinants of cysteine string protein modulation of N-type calcium channels
Linda C. Miller,
Leigh Anne Swayne,
Jason G. Kay,
Zhong-Ping Feng,
Scott E. Jarvis,
Gerald W. Zamponi,
and
Janice E.A. Braun*
* Author for correspondence (e-mail: braunj{at}ucalgary.ca)
Cysteine string proteins (CSPs) are secretory vesicle chaperones that are important for neurotransmitter release. We have previously reported an interaction of CSP with both heterotrimeric GTP-binding proteins (G proteins) and N-type calcium channels that results in a tonic G protein inhibition of the channels. In this report we directly demonstrate that two separate regions of CSP associate with G proteins. The N-terminal binding site of CSP, which includes the J domain, binds G
subunits but not G
subunits whereas the C terminal binding site of CSP associates with either free G
subunits or G
in complex with G
. The interaction of either binding site of CSP (CSP1-82 or CSP83-198) with G proteins elicits robust tonic inhibition of N-type calcium channel activity. However, CSP1-82 inhibition and CSP83-198 inhibition of calcium channels occur through distinct mechanisms. Calcium channel inhibition by CSP83-198 (but not CSP1-82) is completely blocked by co-expression of the synaptic protein interaction site (synprint) of the N-type channel, indicating that CSP83-198 inhibition is dependent on a physical interaction with the calcium channel. These results suggest that distinct binding sites of CSP can play a role in modulating G protein function and G protein inhibition of calcium channels.

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