Effects of Monovalent Anions on a Temperature-Dependent Heat Capacity Change for Escherichia coli SSB Tetramer Binding to Single-Stranded DNA
- 1 April 2006
- journal article
- research article
- Published by American Chemical Society (ACS) in Biochemistry
- Vol. 45 (16), 5190-5205
- https://doi.org/10.1021/bi052543x
Abstract
We have previously shown that the linkage of temperature-dependent protonation and DNA base unstacking equilibria contribute significantly to both the negative enthalpy change (ΔHobs) and the negative heat capacity change (ΔCp,obs) for Escherichia coli SSB homotetramer binding to single-stranded (ss) DNA. Using isothermal titration calorimetry we have now examined ΔHobs over a much wider temperature range (5−60 °C) and as a function of monovalent salt concentration and type for SSB binding to (dT)70 under solution conditions that favor the fully wrapped (SSB)65 complex (monovalent salt concentration ≥0.20 M). Over this wider temperature range we observe a strongly temperature-dependent ΔCp,obs. The ΔHobs decreases as temperature increases from 5 to 35 °C (ΔCp,obs 0). Both salt concentration and anion type have large effects on ΔHobs and ΔCp,obs. These observations can be explained by a model in which SSB protein can undergo a temperature- and salt-dependent conformational transition (below 35 °C), the midpoint of which shifts to higher temperature (above 35 °C) for SSB bound to ssDNA. Anions bind weakly to free SSB, with the preference Br- > Cl- > F-, and these anions are then released upon binding ssDNA, affecting both ΔHobs and ΔCp,obs. We conclude that the experimentally measured values of ΔCp,obs for SSB binding to ssDNA cannot be explained solely on the basis of changes in accessible surface area (ASA) upon complex formation but rather result from a series of temperature-dependent equilibria (ion binding, protonation, and protein conformational changes) that are coupled to the SSB−ssDNA binding equilibrium. This is also likely true for many other protein−nucleic acid interactions.Keywords
This publication has 73 references indexed in Scilit:
- The Salt-dependence of a Protein–Ligand Interaction: Ion–Protein Binding EnergeticsJournal of Molecular Biology, 2005
- The effects of salt on the TATA binding protein-DNA interaction from a hyperthermophilic archaeonJournal of Molecular Biology, 1998
- Thermodynamics of specific and non-specific DNA binding by the c-myb DNA-binding domainJournal of Molecular Biology, 1998
- Co-operative Binding of Escherichia coli SSB Tetramers to Single-stranded DNA in the (SSB)35 Binding ModeJournal of Molecular Biology, 1994
- Linkage of pH, Anion and Cation Effects in Protein-Nucleic Acid Equilibria: Escherichia coli SSB Protein-Single Stranded Nucleic Acid InteractionsJournal of Molecular Biology, 1994
- Role of the hydrophobic effect in stability of site-specific protein-DNA complexesJournal of Molecular Biology, 1989
- Salt-dependent changes in the DNA binding co-operativity of Escherichia coli single strand binding proteinJournal of Molecular Biology, 1986
- Interactions of bacteriophage T4-coded gene 32 protein with nucleic acidsJournal of Molecular Biology, 1981
- Ion effects on ligand-nucleic acid interactionsJournal of Molecular Biology, 1976
- Extension of the theory of linked functions to incorporate the effects of protein hydrationJournal of Molecular Biology, 1969