title: Calcium ion binding properties and the effect of phosphorylation on the intrinsically disordered Starmaker protein.
abstract: Starmaker (Stm) is an intrinsically disordered protein (IDP) involved in otolith biomineralization in Danio rerio. Stm controls calcium carbonate crystal formation in vivo and in vitro. Phosphorylation of Stm affects its biomineralization properties. This study examined the effects of calcium ions and phosphorylation on the structure of Stm. We have shown that CK2 kinase phosphorylates 25 or 26 residues in Stm. Furthermore, we have demonstrated that Stm's affinity for calcium binding is dependent on its phosphorylation state. Phosphorylated Stm (StmP) has an estimated 30 ± 1 calcium binding sites per protein molecule with a dissociation constant (KD) of 61 ± 4 μM, while the unphosphorylated protein has 28 ± 3 sites and a KD of 210 ± 22 μM. Calcium ion binding induces a compaction of the Stm molecule, causing a significant decrease in its hydrodynamic radius and the formation of a secondary structure. The screening effect of Na(+) ions on calcium binding was also observed. Analysis of the hydrodynamic properties of Stm and StmP showed that Stm and StmP molecules adopt the structure of native coil-like proteins.
authors.affiliation: Wrocław University of Technology , Faculty of Chemistry, Department of Biochemistry, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Wojtas
authors.affiliation: Wrocław University of Technology , Faculty of Chemistry, Department of Biochemistry, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland.
authors.forename: Rafał
authors.initials: R
authors.lastname: Hołubowicz
authors.affiliation: Wrocław University of Technology , Faculty of Chemistry, Department of Biochemistry, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland.
authors.forename: Monika
authors.initials: M
authors.lastname: Poznar
authors.affiliation: Wrocław University of Technology , Faculty of Chemistry, Department of Biochemistry, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Maciejewska
authors.affiliation: Wrocław University of Technology , Faculty of Chemistry, Department of Biochemistry, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Ożyhar
authors.affiliation: Wrocław University of Technology , Faculty of Chemistry, Department of Biochemistry, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Dobryszycki
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002119:Calcium Carbonate / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D047390:Casein Kinase II / Q000378:metabolism; D057446:Hydrodynamics; D064267:Intrinsically Disordered Proteins / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D008903:Minerals / Q000378:metabolism; D008958:Models, Molecular; D010037:Otolithic Membrane / Q000378:metabolism; D010766:Phosphorylation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D015027:Zebrafish / Q000378:metabolism; D029961:Zebrafish Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; D064267:Intrinsically Disordered Proteins; D008903:Minerals; D029961:Zebrafish Proteins; C478248:stm protein, zebrafish; D047390:Casein Kinase II; D002119:Calcium Carbonate; D002118:Calcium