title: Sequential phosphorylation of adjacent serine residues on the N-terminal region of cardiac troponin-I: structure-activity implications of ordered phosphorylation.
abstract: We have used NMR spectroscopy to monitor the phosphorylation of a peptide corresponding to the N-terminal region of human cardiac troponin-I (residues 17-30), encompassing the two adjacent serine residues of the dual phosphorylation site. An ordered incorporation of phosphate catalysed by PKA was observed, with phosphorylation of Ser-24 preceding that of Ser-23. Diphosphorylation induced a conformational transition in this region, involving the specific association of the Arg-22 and Ser-24P side-chains, and maximally stabilised when both phosphoserines were in the di-anionic form. The results suggest that the second phosphorylation at Ser-23 of cardiac troponin-I is of particular significance in the mechanism by which adrenaline regulates the calcium sensitivity of the myofibrillar actomyosin Mg-ATPase.
authors.affiliation: School of Biochemistry, University of Birmingham, Edgbaston, UK.
authors.forename: P G
authors.initials: PG
authors.lastname: Quirk
authors.forename: V B
authors.initials: VB
authors.lastname: Patchell
authors.forename: Y
authors.initials: Y
authors.lastname: Gao
authors.forename: B A
authors.initials: BA
authors.lastname: Levine
authors.forename: S V
authors.initials: SV
authors.lastname: Perry
mesh_terms: D000595:Amino Acid Sequence; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009206:Myocardium / Q000737:chemistry*; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D011487:Protein Conformation; D012694:Serine / Q000737:chemistry / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014336:Troponin / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D010446:Peptide Fragments; D014336:Troponin; D012694:Serine