Effects of ionic strength and state of assembly on kinetics of hydrogen exchange of calf thymus histones

Abstract

The kinetics of hydrogen exchange of calf thymus histone H2A-H2B dimers and (H3-H4)2 tetramers at pH 7 have been examined at low (0.16 M NaCl) and high (2 M NaCl) ionic strengths and after incorporation into (H2A-H2B-H3-H4)2 octamers. The similarity of the results for both species is noteworthy. Approximately 60% of the backbone amide protons are detectable in both low and high salt, and at least three kinetic phases can be distinguished. Increasing the ionic strength from 0.16 to 2 M accelerates exchange of some of the rapidly exchanging protons in both dimers and tetramers, while slowing exchange of others. Exchange of the more slowly exchanging protons is virtually unaffected. Incorporation of dimers into octamers accelerates exchange of approximately 40 protons to such an extent that they can no longer be detected. The effects of assembly upon the tetramer are qualitatively similar. These results indicate that both high ionic strengths and assembly destabilize some regions of the structure while stabilizing others. For both dimers and tetramers, the effects of ionic strength are dramatic, while those of assembly are more subtle. Higher resolution studies aimed at identifying the responsive protons would be of interest.

Conformational states of the nicotinic acetylcholine receptor from Torpedo californica induced by the binding of agonists, antagonists, and local anesthetics. Equilibrium measurements using tritium-hydrogen exchange

“…Including more than two kinetic classes or changing the number of iterations did not improve the quality of these fits. The variance in some of the parameters is somewhat high, particularly for the fast class, but these variance values are no higher than those reported in earlier tritium-hydrogen exchange studies (Lennick & Allewell, 1981;McCarthy et al, 1984), when errors are reported at all.…”

“…turn reflect the overall conformation of the protein Englander, 1975;Allewell, 1983). This technique has been used to measure the relatively gross conformational transitions of the histone subunits observed upon alteration of the ionic strength (McCarthy et al, 1984), as well as the more subtle allosteric transitions of hemoglobin (Englander & Mauel, 1972) and Escherichia coli aspartate transcarbamylase (Lennick & Allewell, 1981; Burz & Allewell, 1986). It has also proved a sensitive assay of conformational flexibility in such membrane proteins as rhodopsin (Osborne, 1976;Downer & Englander, 1977) and bacteriorhodopsin ; Konishi & Packer, 1977).…”

Quantitative Disassembly and Reassembly of Human Papillomavirus Type 11 Viruslike Particles In Vitro

“…The observation that VLPs form spontaneously from capsomeres at high-ionic-strength conditions but are thermodynamically unstable in a reducing environment at physiological salt concentrations suggests a possible model for viral disassembly during infection. Viral capsids form in the nucleus, where host and viral DNA may create a local, high-ionicstrength environment, as has been observed in studies of histone conformation and assembly (30). Disulfide bonds may then form in the nucleus or upon release of the virion from the cell.…”

Thiol reactivity of histone H3 in soluble and DNA-associated histone complexes: evidence for allosteric and torsional regulation

“…Previous work from our laboratory has demonstrated that upon the interaction of dimers with tetramers there is a net loss of protons from the complex (Benedict et al, 1984), cooperativity in the binding of a second dimer to the hexameric (H3-H4)2-H2A-H2B complex (Eickbush & Moudrianakis, 1978), and a change in the kinetics of hydrogen exchange of tetramers (McCarthy et al, 1984). These phenomena indicate that changes within the tetramer occur upon the binding of dimers and therefore predict that the thiol reactivity of the tetramer may be modulated by association of these subunits.…”