title: Backbone dynamics of SDF-1alpha determined by NMR: interpretation in the presence of monomer-dimer equilibrium.
abstract: SDF-1alpha is a member of the chemokine family implicated in various reactions in the immune system. The interaction of SDF-1alpha with its receptor, CXCR4, is responsible for metastasis of a variety of cancers. SDF-1alpha is also known to play a role in HIV-1 pathogenesis. The structures of SDF-1alpha determined by NMR spectroscopy have been shown to be monomeric while X-ray structures are dimeric. Biochemical data and in vivo studies suggest that dimerization is likely to be important for the function of chemokines. We report here the dynamics of SDF-1alpha determined through measurement of main chain (15)N NMR relaxation data. The data were obtained at several concentrations of SDF-1alpha and used to determine a dimerization constant of approximately 5 mM for a monomer-dimer equilibrium. The dimerization constant was subsequently used to extrapolate values for the relaxation data corresponding to monomeric SDF-1alpha. The experimental relaxation data and the extrapolated data for monomeric SDF-1alpha were analyzed using the model free approach. The model free analysis indicated that SDF-1alpha is rigid on the nano- to picosecond timescale with flexible termini. Several residues involved in the dimer interface display slow micro- to millisecond timescale motions attributable to chemical exchange such as monomer-dimer equilibrium. NMR relaxation measurements are shown to be applicable for studying oligomerization processes such as the dimerization of SDF-1alpha.
authors.affiliation: Department of Biochemistry and Protein Engineering Network of Centres of Excellence, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
authors.forename: Olga K
authors.initials: OK
authors.lastname: Baryshnikova
authors.forename: Brian D
authors.initials: BD
authors.lastname: Sykes
mesh_terms: D000595:Amino Acid Sequence; D054377:Chemokine CXCL12; D018925:Chemokines / Q000737:chemistry; D019743:Chemokines, CXC / Q000737:chemistry*; D019281:Dimerization; D006801:Humans; D008958:Models, Molecular; D008962:Models, Theoretical; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D009994:Osmolar Concentration; D011485:Protein Binding
chemical_list: C515255:CXCL12 protein, human; D054377:Chemokine CXCL12; D018925:Chemokines; D019743:Chemokines, CXC