Study On The Domains Of UNC-31/CAPS Protein In Docking Step By Total Internal Reflection Fluorescence Microscopy

Celluar secretion processes via vesicular fusion with plasma membrane are critically important for a variety of life functions, and tightly related to some serious diseases such as hyperthyroidism, gigantism, and myasthenia gravis. There are two types of vesicles: synaptic vesicles (SVs) and dense core vesicles (DCVs). SVs contain classical transmitters like glutamate, GABA etc, while DCVs are responsible for the release of hormones, neuropeptides and monoamines. Many similarities do exit between the two kinds of vesicles. Both of two classes of vesicles require Ca2+ to trigger fusion, they shared similar exocytotic molecular michanery which is consisted of SNARE proteins (soluble Nethylmaleimide-sensitive factor attachment protein receptor) and synaptotagmin, and their exocytotic processes are regulated by similar mechanism. Despite these similarities in the fusion machinery for both vesicle types, there are differences in the kinetics of exocytosis and in the physiological regulation of release. For example, SVs usually happen at active zones, but DCVs are excluded from these areas. These differences suggest that there are proteins and mechanisms that are distinct for SV and DCV exocytosis.UNC-31/CAPS (Ca2+-dependent activator protein for secretion) protein is reported to be an important regulator for exocytosis of DCVs and SVs. But the mechanism is still not clear. UNC-31 possesses four structural and functional domains, C2, PH (pleckstrin homology), MHD (Munc homologue domain) and DCV binding domain. This structural characteristic is key to revel the mechanism underlying the function of Unc-31. We used cultured embryonic ALA neuron of Caenorhabditis elegans as cell model. Employing total internal reflection fluorescence microscopy (TIRFM) and molecular biological techniques, we analyzed the functions of four domains of Unc-31 in the docking and priming of DCVs. Our data suggest that UNC-31/CAPS plays an important role in docking events of DCVs, and the four domains are indispensable for its function.