A Syntaxin 1, Gαo, and N-Type Calcium Channel Complex at a Presynaptic Nerve Terminal: Analysis by Quantitative Immunocolocalization

• Published in: The Journal of neuroscience Vol. 24; no. 16; pp. 4070 - 4081
• Main Authors: Li, Qi, Lau, Anthony, Morris, Terence J., Guo, Lin, Fordyce, Christopher B., Stanley, Elise F.
• Format: Journal Article
• Language: English
• Published: Society for Neuroscience 21.04.2004
• Subjects: Cellular/Molecular
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.0346-04.2004

Presynaptic Ca V 2.2 (N-type) calcium channels are subject to modulation by interaction with syntaxin 1 and by a syntaxin 1-sensitive Gα O G-protein pathway. We used biochemical analysis of neuronal tissue lysates and a new quantitative test of colocalization by intensity correlation analysis at the giant calyx-type presynaptic terminal of the chick ciliary ganglion to explore the association of Ca V 2.2 with syntaxin 1 and Gα O . Ca V 2.2 could be localized by immunocytochemistry (antibody Ab571) in puncta on the release site aspect of the presynaptic terminal and close to synaptic vesicle clouds. Syntaxin 1 coimmunoprecipitated with Ca V 2.2 from chick brain and chick ciliary ganglia and was widely distributed on the presynaptic terminal membrane. A fraction of the total syntaxin 1 colocalized with the Ca V 2.2 puncta, whereas the bulk colocalized with MUNC18-1. Gα O, whether in its trimeric or monomeric state, did not coimmunoprecipitate with Ca V 2.2, MUNC18-1, or syntaxin 1. However, the G-protein exhibited a punctate staining on the calyx membrane with an intensity that varied in synchrony with that for both Ca channels and syntaxin 1 but only weakly with MUNC18-1. Thus, syntaxin 1 appears to be a component of two separate complexes at the presynaptic terminal, a minor one at the transmitter release site with Ca V 2.2 and Gα O , as well as in large clusters remote from the release site with MUNC18-1. These syntaxin 1 protein complexes may play distinct roles in presynaptic biology.