title: E. coli SSB tetramer binds the first and second molecules of (dT)(35) with heat capacities of opposite sign.
abstract: We have previously shown that formation of a 1:1 fully wrapped complex of Escherichia coli SSB tetramer with (dT)(70) displays a temperature-dependent sign reversal of the binding heat capacity (ΔC(P)). Here we examine SSB binding to shorter oligodeoxynucleotides ((dX)(35)) to probe whether this effect requires binding of one or two (dX)(35) molecules per SSB tetramer. We find that the ΔC(P) for the first molecule of (dX)(35) is always negative. However, a sign reversal of ΔC(P) from negative to positive occurs with increasing temperature for binding of the second (dX)(35). This striking behavior of ΔC(P) for the second (dX)(35) appears linked to conformational changes within the ssDNA-SSB complex that are required to form a fully wrapped (SSB)(65) binding mode. These results also underscore that binding heat capacities of macromolecular interactions have multiple origins that cannot be understood simply on the basis of examining static structures.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, United States.
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Kozlov
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Lohman
mesh_terms: D004277:DNA, Single-Stranded / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D009838:Oligodeoxyribonucleotides / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization; D012492:Salts / Q000378:metabolism; D012965:Sodium Chloride / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D009838:Oligodeoxyribonucleotides; C476430:SSB protein, E coli; D012492:Salts; D012965:Sodium Chloride