Ca2+–sensor Neurocalcin Delta Modulated Site in ROS–GC1–linked Signaling Pathway in Certain Ganglion Cells

Abstract

Abstract: : Purpose:Previous studies established the presence of the Ca²⁺–modulated neurocalcin delta/ROS–GC1 transduction machinery in the inner retinal neurons. The present study was designed to determine the neurocalcin delta–modulatory site in ROS–GC1 signaling pathway and localize the pathway in the inner retina. Methods:Mutagenesis/in vitro reconstitution experiments, western analyses, surface plasmon resonance spectroscopy and immunostaining. Results:In vitro reconstitution experiments were carried out to test the response of different deletion mutants of ROS–GC1 to neurocalcin delta. Deletion of aa 965–1054 had no effect on the Ca²⁺–dependent stimulation of the cyclase and the bacterially expressed ROS–GC1 fragment aa 965–1054 did not directly bind neurocalcin delta. Immunostaining analyses showed that ROS–GC1 and neurocalcin delta are present in certain ganglion cells. Thus, in response to Ca²⁺, neurocalcin delta binds to the specified domain of ROS–GC1 and activates the cyclase. Conclusions:In retina, ROS–GC1 is modulated by four Ca²⁺–sensor proteins: GCAP1, GCAP2, S100 beta and neurocalcin delta. Ca²⁺–dependent activation of ROS–GC1 by neurocalcin delta occurs via a unique cyclase domain – aa 733– 964. The pathway appears to be functional in a sub–population of large ganglion cells.

Keywords: calcium • ganglion cells