title: Reversible and fast association equilibria of a molecular chaperone, gp57A, of bacteriophage T4.
abstract: The association of a molecular chaperone, gp57A, of bacteriophage T4, which facilitates formation of the long and short tail fibers, was investigated by analytical ultracentrifugation, differential scanning microcalorimetry, and stopped-flow circular dichroism (CD) to establish the association scheme of the protein. Gp57A is an oligomeric alpha-helix protein with 79 amino acids. Analysis of the sedimentation velocity data by direct boundary modeling with Lamm equation solutions together with a more detailed boundary analysis incorporating association schemes led us to conclude that at least three oligomeric species of gp57A are in reversible and fast association equilibria and that a 3(mer)-6(mer)-12(mer) model described the data best. On the other hand, differential scanning microcalorimetry revealed a highly reversible two-step transition of dissociation/denaturation, both of which accompanied decrease in CD at 222 nm. The melting curve analysis revealed that it is consistent with a 6(mer)-3(mer)-1(mer) model. The refolding/association kinetics of gp57A measured by stopped-flow CD was consistent with the interpretation that the bimolecular reaction from trimer to hexamer was preceded by a fast alpha-helix formation in the dead-time. Trimer or hexamer is likely the functional oligomeric state of gp57A.
mesh_terms: D002152:Calorimetry, Differential Scanning / Q000379:methods*; D002499:Centrifugation, Density Gradient / Q000379:methods*; D002942:Circular Dichroism / Q000379:methods*; D019281:Dimerization; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046911:Macromolecular Substances; D008956:Models, Chemical; D018832:Molecular Chaperones / Q000737:chemistry*; D008970:Molecular Weight; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D020033:Protein Isoforms / Q000737:chemistry; D017433:Protein Structure, Secondary; D013696:Temperature; D014764:Viral Proteins / Q000737:chemistry*
chemical_list: C104876:Gp57A protein, Bacteriophage T4; D046911:Macromolecular Substances; D018832:Molecular Chaperones; D020033:Protein Isoforms; D014764:Viral Proteins