Karl-Wilhelm Koch

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In visual transduction, guanylate cyclase-activating proteins (GCAPs) activate the membrane-bound guanylate cyclase 1 (ROS-GC1) to synthesize cGMP under conditions of low cytoplasmic [Ca2+]free. GCAPs are neuronal Ca2+-binding proteins with three functional EF-hands and a consensus site for N-terminal myristoylation. GCAP-1 and GCAP-2 regulated ROS-GC1(More)
The GUCA1A gene encodes the guanylate cyclase activating protein 1 (GCAP1) of mammalian rod and cone photoreceptor cells, which is involved in the Ca2+-dependent negative feedback regulation of membrane bound guanylate cyclases in the retina. Mutations in the GUCA1A gene have been associated with different forms of cone dystrophies leading to impaired cone(More)
In rod phototransduction, cyclic GMP synthesis by membrane bound guanylate cyclase ROS-GC1 is under Ca(2+)-dependent negative feedback control mediated by guanylate cyclase-activating proteins, GCAP-1 and GCAP-2. The cellular concentration of GCAP-1 and GCAP-2 approximately sums to the cellular concentration of a functional ROS-GC1 dimer. Both GCAPs(More)
The rod outer segment membrane guanylate cyclase type 1 (ROS-GC1), originally identified in the photoreceptor outer segments, is a member of the subfamily of Ca(2+)-modulated membrane guanylate cyclases. In phototransduction, its activity is tightly regulated by its two Ca(2+)-sensor protein parts, GCAP1 and GCAP2. This study maps the GCAP2-modulatory site(More)
This study documents the identity of a calcium- regulated membrane guanylate cyclase transduction system in the photoreceptor-bipolar synaptic region. The guanylate cyclase is the previously characterized ROS-GC1 from the rod outer segments and its modulator is S100beta. S100beta senses increments in free Ca(2+) and stimulates the cyclase. Specificity of(More)
Guanylate cyclase-activating proteins (GCAPs) are neuronal calcium sensors that activate membrane bound guanylate cyclases (EC of vertebrate photoreceptor cells when cytoplasmic Ca2+ decreases during illumination. GCAPs contain four EF-hand Ca2+-binding motifs, but the first EF-hand is nonfunctional. It was concluded that for GCAP-2, the loss of(More)
Calcium-signaling in cells requires a fine-tuned system of calcium-transport proteins involving ion channels, exchangers, and ion-pumps but also calcium-sensor proteins and their targets. Thus, control of physiological responses very often depends on incremental changes of the cytoplasmic calcium concentration, which are sensed by calcium-binding proteins(More)
Rod outer segment membrane guanylate cyclase (ROS-GC) transduction system is a central component of the Ca(2+)-sensitive phototransduction machinery. The system is composed of two parts: Ca(2+) sensor guanylate cyclase activating protein (GCAP) and ROS-GC. GCAP senses Ca(2+) impulses and inhibits the cyclase. This operational feature of the cyclase is(More)
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 Ca(2+)-binding proteins named GC-activating proteins that operate as Ca2+ sensors and enable cyclases to respond to changes of intracellular Ca2+after(More)
Cholesterol-rich membranes or detergent-resistant membranes (DRMs) have recently been isolated from bovine rod outer segments and were shown to contain several signaling proteins such as, for example, transducin and its effector, cGMP-phosphodiesterase PDE6. Here we report the presence of rhodopsin kinase and recoverin in DRMs that were isolated in either(More)