Calcium-modulated ciliary membrane guanylate cyclase transduction machinery: constitution and operational principles.

Odorant transduction is a biochemical process by which the odorant signal generates the electric signal. The cilia of the olfactory neuroepithelium are the sites of this process. This study documents the detailed biochemical, structural and functional description of an odorant-responsive Ca2+ -modulated membrane guanylate cyclase transduction machinery in the cilia. Myristoylated (myr)-neurocalcin delta is the Ca2+ -sensor component and the cyclase, ONE-GC, the transduction component of the machinery. Myr-neurocalcin delta senses increments in free Ca2+, binds to a defined domain of ONE-GC and stimulates the cyclase. The findings enable the formulation of an odorant transduction model in which three pivotal signaling components--Ca2+, myr-neurocalcin delta and ONE-GC--of the transduction machinery are locked. A glaring feature of the model is that its Ca2+ -dependent operational principle is opposite to the phototransduction model.