title: Retina specific GCAPs in zebrafish acquire functional selectivity in Ca2+-sensing by myristoylation and Mg2+-binding.
abstract: Zebrafish photoreceptor cells express six guanylate cyclase-activating proteins (zGCAPs) that share a high degree of amino acid sequence homology, but differ in Ca(2+)-binding properties, Ca(2+)-sensitive target regulation and spatial-temporal expression profiles. We here study a general problem in cellular Ca(2+)-sensing, namely how similar Ca(2+)-binding proteins achieve functional selectivity to control finely adjusted cellular responses. We investigated two parameters of critical importance for the trigger and switch function of guanylate cyclase-activating proteins: the myristoylation status and the occupation of Ca(2+)-binding sites with Mg(2+). All zGCAPs can be myristoylated in living cells using click chemistry. Myristoylation does not facilitate membrane binding of zGCAPs, but it significantly modified the regulatory properties of zGCAP2 and zGCAP5. We further determined for all zGCAPs at least two binding sites exhibiting high affinities for Ca(2+) with KD values in the submicromolar range, whereas for other zGCAPs (except zGCAP3) the affinity of the third binding site was in the micromolar range. Mg(2+) either occupied the low affinity Ca(2+)-binding site or it shifted the affinities for Ca(2+)-binding. Hydrodynamic properties of zGCAPs are more influenced by Ca(2+) than by Mg(2+), although to a different extent for each zGCAP. Posttranslational modification and competing ion-binding can tailor the properties of similar Ca(2+)-sensors.
authors.affiliation: Department of Neurosciences, Biochemistry Group, University of Oldenburg, D-26111-Oldenburg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Sulmann
authors.affiliation: Department of Neurosciences, Biochemistry Group, University of Oldenburg, D-26111-Oldenburg, Germany.
authors.forename: Farina
authors.initials: F
authors.lastname: Vocke
authors.affiliation: Department of Neurosciences, Biochemistry Group, University of Oldenburg, D-26111-Oldenburg, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Scholten
authors.affiliation: Department of Neurosciences, Biochemistry Group, University of Oldenburg, D-26111-Oldenburg, Germany.
authors.forename: Karl-Wilhelm
authors.initials: KW
authors.lastname: Koch
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002460:Cell Line; D051604:Guanylate Cyclase-Activating Proteins / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D008274:Magnesium / Q000378:metabolism*; D019814:Myristic Acid / Q000378:metabolism; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D015027:Zebrafish / Q000378:metabolism*; D029961:Zebrafish Proteins / Q000378:metabolism
chemical_list: D002135:Calcium-Binding Proteins; D051604:Guanylate Cyclase-Activating Proteins; D029961:Zebrafish Proteins; D019814:Myristic Acid; D008274:Magnesium; D002118:Calcium