Differential Ca(2+) sensor guanylate cyclase activating protein modes of photoreceptor rod outer segment membrane guanylate cyclase signaling.
Photoreceptor ROS-GC1 (rod outer segment membrane guanylate cyclase) is a vital component of phototransduction. It is a bimodal Ca(2+) signal transduction switch, operating between 20 and ∼1000 nM. Modulated by Ca(2+) sensors guanylate cyclase activating proteins 1 and 2 (GCAP1 and GCAP2, respectively), decreasing [Ca(2+)](i) from 200 to 20 nM progressively turns it "on", as does the modulation by the Ca(2+) sensor S100B, increasing [Ca(2+)](i) from 100 to 1000 nM. The GCAP mode plays a vital role in phototransduction in both rods and cones and the S100B mode in the transmission of neural signals to cone ON-bipolar cells. Through a programmed domain deletion, expression, in vivo fluorescence spectroscopy, and in vitro reconstitution experiments, this study demonstrates that the biochemical mechanisms modulated by two GCAPs in Ca(2+) signaling of ROS-GC1 activity are totally different. (1) They involve different structural domains of ROS-GC1. (2) Their signal migratory pathways are opposite: GCAP1 downstream and GCAP2 upstream. (3) Importantly, the isolated catalytic domain, translating the GCAP-modulated Ca(2+) signal into the generation of cyclic GMP, in vivo, exists as a homodimer, the two subunits existing in an antiparallel conformation. Furthermore, the findings demonstrate that the N-terminally placed signaling helix domain is not required for the catalytic domain's dimeric state. The upstream GCAP2-modulated pathway is the first of its kind to be observed for any member of the membrane guanylate cyclase family. It defines a new model of Ca(2+) signal transduction.
The Unit of Regulatory and Molecular Biology, Salus University, Elkins Park, PA 19027, USA. tduda@salus.edu
Teresa
T
Duda
Alexandre
A
Pertzev
Rameshwar K
RK
Sharma
D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000201:enzymology*; D002522:Chlorocebus aethiops; D005786:Gene Expression Regulation; D006162:Guanylate Cyclase / Q000235:genetics / Q000378:metabolism*; D051604:Guanylate Cyclase-Activating Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*; D015398:Signal Transduction
C496736:GUCA1A protein, human; C496739:GUCA1B protein, human; D051604:Guanylate Cyclase-Activating Proteins; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C110715:guanylate cyclase 1; D006162:Guanylate Cyclase