title: Experimentally exploring the conformational space sampled by domain reorientation in calmodulin.
abstract: The conformational space sampled by the two-domain protein calmodulin has been explored by an approach based on four sets of NMR observables obtained on Tb(3+)- and Tm(3+)-substituted proteins. The observables are the pseudocontact shifts and residual dipolar couplings of the C-terminal domain when lanthanide substitution is at the N-terminal domain. Each set of observables provides independent information on the conformations experienced by the molecule. It is found that not all sterically allowed conformations are equally populated. Taking the N-terminal domain as the reference, the C-terminal domain preferentially resides in a region of space inscribed in a wide elliptical cone. The axis of the cone is tilted by approximately 30 degrees with respect to the direction of the N-terminal part of the interdomain helix, which is known to have a flexible central part in solution. The C-terminal domain also undergoes rotation about the axis defined by the C-terminal part of the interdomain helix. Neither the extended helix conformation initially observed in the solid state for free calcium calmodulin nor the closed conformation(s) adopted by calcium calmodulin either alone or in its adduct(s) with target peptide(s) is among the most preferred ones. These findings are unique, both in terms of structural information obtained on a biomolecule that samples multiple conformations and in terms of the approach developed to achieve the results. The same approach is in principle applicable to other multidomain proteins, as well as to multiple interaction modes between two macromolecular partners.
authors.affiliation: Centre for Magnetic Resonance and Department of Chemistry, University of Florence, Via Luigi Sacconi 6, I-50019 Sesto Fiorentino, Italy. bertini@cerm.unifi.it
authors.forename: Ivano
authors.initials: I
authors.lastname: Bertini
authors.forename: Cristina
authors.initials: C
authors.lastname: Del Bianco
authors.forename: Ioannis
authors.initials: I
authors.lastname: Gelis
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Katsaros
authors.forename: Claudio
authors.initials: C
authors.lastname: Luchinat
authors.forename: Giacomo
authors.initials: G
authors.lastname: Parigi
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Peana
authors.forename: Alessandro
authors.initials: A
authors.lastname: Provenzani
authors.forename: Maria Antonietta
authors.initials: MA
authors.lastname: Zoroddu
mesh_terms: D000818:Animals; D016880:Anisotropy; D002147:Calmodulin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
chemical_list: D002147:Calmodulin