title: Structure and dimerization of translation initiation factor aIF5B in solution.
abstract: Translation initiation factor 5B (IF5B) is required for initiation of protein synthesis. The solution structure of archaeal IF5B (aIF5B) was analysed by small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) and was indicated to be in both monomeric and dimeric form. Sedimentation equilibrium (SE) analytical ultracentrifugation (AUC) of aIF5B indicated that aIF5B forms irreversible dimers in solution but only to a maximum of 5.0-6.8% dimer. Sedimentation velocity (SV) AUC at higher speed also indicated the presence of two species, and the sedimentation coefficients s(20,w)(0) were determined to be 3.64 and 5.51±0.29 S for monomer and dimer, respectively. The atomic resolution (crystallographic) structure of aIF5B (Roll-Mecak et al. [6]) was used to model monomer and dimer, and theoretical sedimentation coefficients for these models were computed (3.89 and 5.63 S, respectively) in good agreement with the sedimentation coefficients obtained from SV analysis. Thus, the structure of aIF5B in solution must be very similar to the atomic resolution structure of aIF5B. SAXS data were acquired in the same buffer with the addition of 2% glycerol to inhibit dimerization, and the resultant monomeric aIF5B in solution did indeed adopt a structure very similar to the one reported earlier for the protein in crystalline form. The p(r) function indicated an elongated conformation supported by a radius of gyration of 37.5±0.2 Å and a maximum dimension of ~130 Å. The effects of glycerol on the formation of dimers are discussed. This new model of aIF5B in solution shows that there are universal structural differences between aIF5B and the homologous protein IF2 from Escherichia coli.
authors.affiliation: Department of Molecular Biology, Aarhus University, Gustav Wieds Vej 10, DK-8000 Aarhus C, Denmark.
authors.forename: Louise Carøe Vohlander
authors.initials: LC
authors.lastname: Rasmussen
authors.forename: Cristiano Luis Pinto
authors.initials: CL
authors.lastname: Oliveira
authors.forename: Olwyn
authors.initials: O
authors.lastname: Byron
authors.forename: Janni Mosgaard
authors.initials: JM
authors.lastname: Jensen
authors.forename: Jan Skov
authors.initials: JS
authors.lastname: Pedersen
authors.forename: Hans Uffe
authors.initials: HU
authors.lastname: Sperling-Petersen
authors.forename: Kim Kusk
authors.initials: KK
authors.lastname: Mortensen
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry*; D008958:Models, Molecular; D010448:Peptide Initiation Factors / Q000737:chemistry*; D011487:Protein Conformation; D055503:Protein Multimerization; D053838:Scattering, Small Angle; D012996:Solutions; D014961:X-Ray Diffraction
chemical_list: D019843:Archaeal Proteins; D010448:Peptide Initiation Factors; D012996:Solutions