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J Cell Sci. 2003 Jul 15;116(Pt 14):2967-74. Epub 2003 Jun 3.

Molecular determinants of cysteine string protein modulation of N-type calcium channels.

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Neuroscience Research Group, Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, T2N 4N1, Canada.


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 Galpha subunits but not Galphabeta subunits whereas the C terminal binding site of CSP associates with either free Galphabeta subunits or Galphabeta in complex with Galpha. 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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