title: Solution structure and backbone dynamics of the defunct domain of calcium vector protein.
abstract: CaVP (calcium vector protein) is a Ca(2+) sensor of the EF-hand protein family which is highly abundant in the muscle of Amphioxus. Its three-dimensional structure is not known, but according to the sequence analysis, the protein is composed of two domains, each containing a pair of EF-hand motifs. We determined recently the solution structure of the C-terminal domain (Trp81-Ser161) and characterized the large conformational and dynamic changes induced by Ca(2+) binding. In contrast, the N-terminal domain (Ala1-Asp86) has lost the capacity to bind the metal ion due to critical mutations and insertions in the two calcium loops. In this paper, we report the solution structure of the N-terminal domain and its backbone dynamics based on NMR spectroscopy, nuclear relaxation, and molecular modeling. The well-resolved three-dimensional structure is typical of a pair of EF-hand motifs, joined together by a short antiparallel beta-sheet. The tertiary arrangement of the two EF-hands results in a closed-type conformation, with near-antiparallel alpha-helices, similar to other EF-hand pairs in the absence of calcium ions. To characterize the internal dynamics of the protein, we measured the (15)N nuclear relaxation rates and the heteronuclear NOE effect in (15)N-labeled N-CaVP at a magnetic field of 11.74 T and 298 K. The domain is mainly monomeric in solution and undergoes an isotropic Brownian rotational diffusion with a correlation time of 7.1 ns, in good agreement with the fluorescence anisotropy decay measurements. Data analysis using a model-free procedure showed that the amide backbone groups in the alpha-helices and beta-strands undergo highly restricted movements on a picosecond to nanosecond time scale. The amide groups in Ca(2+) binding loops and in the linker fragment also display rapid fluctuations with slightly increased amplitudes.
authors.affiliation: INSERM U350 and Institut Curie-Recherche, Centre Universitaire, Bâtiments 110-112, 91405 Orsay Cedex, France.
authors.forename: I
authors.initials: I
authors.lastname: Théret
authors.forename: S
authors.initials: S
authors.lastname: Baladi
authors.forename: J A
authors.initials: JA
authors.lastname: Cox
authors.forename: J
authors.initials: J
authors.lastname: Gallay
authors.forename: H
authors.initials: H
authors.lastname: Sakamoto
authors.forename: C T
authors.initials: CT
authors.lastname: Craescu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D002816:Chordata, Nonvertebrate / Q000737:chemistry; D018360:Crystallography, X-Ray; D020832:EF Hand Motifs; D005454:Fluorescence Polarization; D008969:Molecular Sequence Data; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D010446:Peptide Fragments / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012996:Solutions; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: C066481:CaVP target protein, amphioxus; D002135:Calcium-Binding Proteins; D009587:Nitrogen Isotopes; D010446:Peptide Fragments; D012996:Solutions