Conformation and reactivity of DNA in the complex with protein. IV. Circular dichroism of poly-L-histidine model complexes with DNA polymers and specificity of the interaction.
The CD study of the DNA-poly-L-histidine complex at high degree of protonation revealed that complex formation is already observable at 2 M NaCl. The influence of salt together with 5 M urea suggests that in addition to electrostatic interactions probably hydrogen bonding may favour specific complexes. Affinity of protonated histidines to AT-rich regions is strongly supported by the complexes formed with (dA.dT)-containing polymers. The psi-type structure occurs with poly(dA-dT)-poly(dA-dT) while poly(dA)-poly(dT) is restricted to form a similar psi-state on interaction with highly protonated poly-L-histidine. Differences in the helix winding properties due to variation in the sequence is suggested as a possible factor in the formation of the psi-type complexes. The mechanism of interaction including hydrogen bonding of histidine side-chains with an AT pair at high degree of protonation and with GC-regions at lower degree of protonation in the polypeptide structure is discussed.
D001665:Binding Sites; D002942:Circular Dichroism; D004247:DNA; D006639:Histidine; D006863:Hydrogen-Ion Concentration; D046911:Macromolecular Substances; D009690:Nucleic Acid Conformation; D009994:Osmolar Concentration; D010455:Peptides; D011485:Protein Binding; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship; D014508:Urea
D046911:Macromolecular Substances; D010455:Peptides; D006639:Histidine; D014508:Urea; D004247:DNA