title: Backbone dynamics of calmodulin studied by 15N relaxation using inverse detected two-dimensional NMR spectroscopy: the central helix is flexible.
abstract: The backbone dynamics of Ca(2+)-saturated recombinant Drosophila calmodulin has been studied by 15N longitudinal and transverse relaxation experiments, combined with 15N(1H) NOE measurements. Results indicate a high degree of mobility near the middle of the central helix of calmodulin, from residue K77 through S81, with order parameters (S2) in the 0.5-0.6 range. The anisotropy observed in the motion of the two globular calmodulin domains is much smaller than expected on the basis of hydrodynamic calculations for a rigid dumbbell type structure. This indicates that, for the purposes of 15N relaxation, the tumbling of the N-terminal (L4-K77) and C-terminal (E82-S147) lobes of calmodulin is effectively independent. A slightly shorter motional correlation time (tau c approximately 6.3 ns) is obtained for the C-terminal domain compared to the N-terminal domain (tau c approximately 7.1 ns), in agreement with the smaller size of the C-terminal domain. A high degree of mobility, with order parameters of approximately 0.5, is also observed in the loop that connects the first with the second EF-hand type calcium binding domain and in the loop connecting the third and fourth calcium binding domain.
authors.affiliation: Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: G
authors.initials: G
authors.lastname: Barbato
authors.forename: M
authors.initials: M
authors.lastname: Ikura
authors.forename: L E
authors.initials: LE
authors.lastname: Kay
authors.forename: R W
authors.initials: RW
authors.lastname: Pastor
authors.forename: A
authors.initials: A
authors.lastname: Bax
mesh_terms: D000818:Animals; D002147:Calmodulin / Q000737:chemistry* / Q000648:ultrastructure; D004331:Drosophila melanogaster; D009682:Magnetic Resonance Spectroscopy; D009038:Motion; D011487:Protein Conformation; D011994:Recombinant Proteins; D012399:Rotation
chemical_list: D002147:Calmodulin; D011994:Recombinant Proteins