CHROMAGRANIN A COILED-COIL STRUCTURE

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Chromogranin A (CHGA) is the major structural protein in the core of neuroendocrine secretory granules. Several physical and optical experiments performed recently by us suggest an extended conformation for the protein. A homology model now suggests that CHGA may assume a coiled-coil structure, much like that of tropomyosin (PDB TPM1, 1c1g A chain). Such a conformation would explain manyof the unusual physical properties of CHGA, and provide a mechanism for dense protein packing within neuroendocrine secretory granule cores. We would like to test experimentally whther CHGA does exist as a coiled-coil, using low angle x-ray scattering. We have in hand purified, recombinant, E. coli-expressed chromogranin A (CHGA) for these experiments. CHGA was purified by 6-His-affinity chromatography, and verified by SDS-PAGE. We have already used this materialfor several physical and biochemical experiments, including circular dichroism spectroscopy, gel filtration to assign molecular weight and Stokes radius, and endocrine (endothelin-releasing) activity on endothelial cells in culture. Here we wish only to do low angle x-ray scattering, to confirm whether a coiled-soil structure exists.