Premium
Thermodynamics and kinetics of the interaction of copper (II) ions with native DNA
Author(s) -
Förster W.,
Bauer E.,
Schütz H.,
Berg H.,
Akimenko N. M.,
Minchenkova L. E.,
Evdokimov Yu. M.,
Varshavsky Ya. M.
Publication year - 1979
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1979.360180311
Subject(s) - chemistry , guanine , dna , crystallography , copper , chelation , ionic strength , ligand (biochemistry) , ion , kinetics , ionic bonding , cytosine , metal ions in aqueous solution , inorganic chemistry , stereochemistry , nucleotide , aqueous solution , organic chemistry , biochemistry , receptor , physics , quantum mechanics , gene
Based on equilibrium binding studies, as well as on kinetic investigations, two types of interactions of Cu 2+ ions with native DNA at low ionic strength could be characterized, namely, a nondenaturing and a denaturing complex formation. During a fast nondenaturing complex formation at low relative ligand concentrations and at low temperatures, different binding sites at the DNA bases become occupied by the metal ions. This type of interaction includes chelate formation of Cu 2+ ions with atoms N (7) of purine bases and the oxygens of the corresponding phosphate groups, chelation between atoms N (7) and O of C (6) of the guanine bases, as well as the formation of specific intestrand crosslink complexes at adjacent G°C pairs of the sequence d GpC. CD spectra of the resulting nondenatured complex (DNA–Cu 2+ ) nat may be interpreted in terms of a conformational change of DNA from the B‐form to a C‐like form on ligand binding. A slow cooperative denaturing complex formation occurs at increased copper concentrations and/or at increased temperatures. The uv absorption and CD spectra of the resulting complex, (DNA–Cu 2+ ) denat , indicate DNA denaturation during this type of interaction. Such a conclusion is confirmed by microcalorimetric measurements, which show that the reaction consumes nearly the same amount of heat as acid denaturation of DNA. From these and the kinetic results, the following mechanism for the denaturing action of the ligands is suggested: binding of Cu 2+ ions to atoms N (3) of the cytosine bases takes place when the cytosines come to the outside of the double helix as a result of statistical fluctuations. After the completion of the binding process, the bases cannot return to their initial positions, and thus local denaturation at the G·C pairs is brought about. The probability of the necessary fluctuations occurring is increased by chelation of Cu 2+ ions between atoms N (7) and O of C (6) of the guanine bases during nondenaturing complex formation, which loosens one of the hydrogen bonds within the G·C pairs, as well as by raising the temperature. The implications of the new binding model, which comprises both the sequence‐specific interstand crosslinks and the described mechanism of denaturing complex formation, are discussed and some predictions are made. The model is also used to explain the different renaturation properties of the denatured complexes of Cu 2+ , Cd 2+ , and Zn 2+ ions with DNA. In temperature‐jump experiments with the nondenatured complex (DNA–Cu 2+ ) nat , a specific kinetic effect is observed, namely, the appearance of a lag in the response to the perturbation. The resulting sigmoidal shape of the kinetic curves is considered to be a consequence of the necessity of disrupting a certain number of the crosslinks existing in the nondenatured complex before the local unwinding of the binding regions (a main step of denaturing complex formation) may proceed.