{"type": "root", "children": [{"type": "t", "text": "<div>\n "}, {"type": "p", "children": [{"type": "t", "text": "\n The GUCY2D gene encodes the retinal membrane guanylyl cyclase‐1 (RetGC1), a key enzyme in the phototransduction cascade whose principal function is to synthesize cyclic GMP (cGMP) in photoreceptor cells. RetGC1 is tightly regulated by Ca²⁺‐binding proteins—primarily by guanylate cyclase activating proteins (GCAP1 and GCAP2)—which adjust its activity in response to fluctuating intracellular Ca²⁺ levels. When Ca²⁺ concentrations fall in the light, GCAPs stimulate RetGC1 to restore cGMP levels and help reestablish the dark state, whereas higher Ca²⁺ concentrations inhibit the cyclase activity. This precise regulation is critical for accurate signal recovery after photon absorption, and accordingly, RetGC1 plays an essential role in controlling the sensitivity and recovery kinetics of rod and cone photoreceptors."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Mutations in GUCY2D are a well‐established cause of inherited retinal dystrophies. In its recessive form, such mutations result in Leber congenital amaurosis type 1 (LCA1), which is predominantly characterized by severely reduced cone function with variable rod preservation. Conversely, dominant mutations, often focused on critical residues such as codon 838, lead to cone or cone‐rod degeneration by altering the enzyme’s catalytic properties and Ca²⁺ sensitivity. These pathogenic variants either induce truncations of essential catalytic domains or cause a gain of function by shifting the Ca²⁺ sensitivity of RetGC1 regulation, thereby disrupting the balance of cGMP synthesis during the phototransduction recovery process."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "4", "end_ref": "6"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Structural studies indicate that domains beyond the catalytic core—such as the dimerization/linker region—play crucial roles in mediating interactions with GCAPs. This region not only influences the enzyme’s tendency to dimerize but also directly affects its sensitivity to Ca²⁺ and its maximal activation by GCAPs. In this context, the specific docking and activation steps, including the proper positioning of GCAPs onto RetGC1, are indispensable for maintaining the dynamic range of photoresponse recovery, and mutations disrupting these interactions can lead to inefficient regulation of cGMP synthesis."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "7", "end_ref": "9"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n In summary, GUCY2D is central to photoreceptor function by encoding RetGC1, which regenerates cGMP to enable light adaptation and recovery. Its activity is finely tuned by Ca²⁺ sensor proteins, and even subtle disruptions in these regulatory mechanisms—whether through altered catalytic activity, dimerization, or GCAP interaction—can result in severe visual impairment. \n "}]}, {"type": "t", "text": "\n</div>"}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Francesca Simonelli, Carmela Ziviello, Francesco Testa, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Clinical and molecular genetics of Leber's congenital amaurosis: a multicenter study of Italian patients."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Invest Ophthalmol Vis Sci (2007)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1167/iovs.07-0068"}], "href": "https://doi.org/10.1167/iovs.07-0068"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "17724218"}], "href": "https://pubmed.ncbi.nlm.nih.gov/17724218"}]}, {"type": "r", "ref": 2, "children": [{"type": "t", "text": "Samuel G Jacobson, Artur V Cideciyan, Igor V Peshenko, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Determining consequences of retinal membrane guanylyl cyclase (RetGC1) deficiency in human Leber congenital amaurosis en route to therapy: residual cone-photoreceptor vision correlates with biochemical properties of the mutants."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Hum Mol Genet (2013)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1093/hmg/dds421"}], "href": "https://doi.org/10.1093/hmg/dds421"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "23035049"}], "href": "https://pubmed.ncbi.nlm.nih.gov/23035049"}]}, {"type": "r", "ref": 3, "children": [{"type": "t", "text": "Li Jiang, Wolfgang Baehr "}, {"type": "b", "children": [{"type": "t", "text": "GCAP1 mutations associated with autosomal dominant cone dystrophy."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Adv Exp Med Biol (2010)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1007/978-1-4419-1399-9_31"}], "href": "https://doi.org/10.1007/978-1-4419-1399-9_31"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "20238026"}], "href": "https://pubmed.ncbi.nlm.nih.gov/20238026"}]}, {"type": "r", "ref": 4, "children": [{"type": "t", "text": "Suzanne Yzer, Bart P Leroy, Elfride De Baere, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Microarray-based mutation detection and phenotypic characterization of patients with Leber congenital amaurosis."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Invest Ophthalmol Vis Sci (2006)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1167/iovs.05-0848"}], "href": "https://doi.org/10.1167/iovs.05-0848"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "16505055"}], "href": "https://pubmed.ncbi.nlm.nih.gov/16505055"}]}, {"type": "r", "ref": 5, "children": [{"type": "t", "text": "Veronique B D Kitiratschky, Robert Wilke, Agnes B Renner, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Mutation analysis identifies GUCY2D as the major gene responsible for autosomal dominant progressive cone degeneration."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Invest Ophthalmol Vis Sci (2008)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1167/iovs.08-1901"}], "href": "https://doi.org/10.1167/iovs.08-1901"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "18487367"}], "href": "https://pubmed.ncbi.nlm.nih.gov/18487367"}]}, {"type": "r", "ref": 6, "children": [{"type": "t", "text": "Igor V Peshenko, Gennadiy P Moiseyev, Elena V Olshevskaya, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Factors that determine Ca2+ sensitivity of photoreceptor guanylyl cyclase. Kinetic analysis of the interaction between the Ca2+-bound and the Ca2+-free guanylyl cyclase activating proteins (GCAPs) and recombinant photoreceptor guanylyl cyclase 1 (RetGC-1)."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Biochemistry (2004)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1021/bi048943m"}], "href": "https://doi.org/10.1021/bi048943m"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "15504042"}], "href": "https://pubmed.ncbi.nlm.nih.gov/15504042"}]}, {"type": "r", "ref": 7, "children": [{"type": "t", "text": "Patrick Zägel, Daniele Dell'Orco, Karl-Wilhelm Koch "}, {"type": "b", "children": [{"type": "t", "text": "The dimerization domain in outer segment guanylate cyclase is a Ca²⁺-sensitive control switch module."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Biochemistry (2013)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1021/bi400288p"}], "href": "https://doi.org/10.1021/bi400288p"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "23815670"}], "href": "https://pubmed.ncbi.nlm.nih.gov/23815670"}]}, {"type": "r", "ref": 8, "children": [{"type": "t", "text": "Igor V Peshenko, Elena V Olshevskaya, Alexander M Dizhoor "}, {"type": "b", "children": [{"type": "t", "text": "Dimerization Domain of Retinal Membrane Guanylyl Cyclase 1 (RetGC1) Is an Essential Part of Guanylyl Cyclase-activating Protein (GCAP) Binding Interface."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Biol Chem (2015)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1074/jbc.M115.661371"}], "href": "https://doi.org/10.1074/jbc.M115.661371"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "26100624"}], "href": "https://pubmed.ncbi.nlm.nih.gov/26100624"}]}, {"type": "r", "ref": 9, "children": [{"type": "t", "text": "Igor V Peshenko, Elena V Olshevskaya, Sunghyuk Lim, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Identification of target binding site in photoreceptor guanylyl cyclase-activating protein 1 (GCAP1)."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Biol Chem (2014)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1074/jbc.M113.540716"}], "href": "https://doi.org/10.1074/jbc.M113.540716"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "24567338"}], "href": "https://pubmed.ncbi.nlm.nih.gov/24567338"}]}]}]}