Expression level and activity profile of membrane bound guanylate cyclase type 2 in rod outer segments |
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Authors: | Helten Andreas Säftel Werner Koch Karl-Wilhelm |
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Institution: | Biochemistry group, Institute of Biology and Environmental Sciences, Faculty V, Carl von Ossietzky University Oldenburg, Oldenburg, Germany |
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Abstract: | Rod and cone cells of the mammalian retina harbor two types of a membrane bound guanylate cyclase (GC), rod outer segment guanylate cyclase type 1 (ROS-GC1) and ROS-GC2. Both enzymes are regulated by small Ca2+-binding proteins named GC-activating proteins that operate as Ca2+ sensors and enable cyclases to respond to changes of intracellular Ca2+after illumination. We determined the expression level of ROS-GC2 in bovine ROS preparations and compared it with the level of ROS-GC1 in ROSs. The molar ratio of a ROS-GC2 dimer to rhodopsin was 1 : 13 200. The amount of ROS-GC1 was 25-fold higher than the amount of ROS-GC2. Heterologously expressed ROS-GC2 was differentially activated by GC-activating protein 1 and 2 at low free Ca2+ concentrations. Mutants of GC-activating protein 2 modulated ROS-GC2 in a manner different from their action on ROS-GC1 indicating that the Ca2+ sensitivity of the Ca2+ sensor is controlled by the mode of target–sensor interaction. |
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Keywords: | guanylate cyclase-activating protein guanylate cyclase light adaptation neuronal Ca2+ sensors phototransduction |
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