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Structural investigations on DNA·protamine complexes
Author(s) -
Herskovits T. T.,
Brahms J.
Publication year - 1976
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.1976.360150408
Subject(s) - protamine , chemistry , circular dichroism , linear dichroism , dna , crystallography , folding (dsp implementation) , vibrational circular dichroism , raman spectroscopy , biochemistry , optics , physics , electrical engineering , engineering , heparin
Protamine·DNA complexes in film and in solution have been investigated by means of infrared linear dichroism, ultraviolet circular dichroism, and laser Raman spectroscopy. At high relative humidity and in solution both infrared linear dichroism and ultraviolet circular dichroism indicate the presence of a modified B form of DNA (designated as B* in our other papers 27,28,46 ). This modified B form is characterized by a change of the orientation of the \documentclass{article}\pagestyle{empty}\begin{document}$ \widehat{OPO} $\end{document} bisector angle by about 4° with respect to the helical axis when compared to the B form of DNA. At decreasing relative humidities the same modified B form is maintained and no structural transitions B → A (or B → C) normally occurring in free DNA were observed. The absence of the A form in these complexes was also confirmed by laser Raman scattering studies of protamine·DNA complexes. On the basis of these results, a model of the protamine·DNA complex is proposed, which suggests that the presence of apolar amino‐acid residues, and probably the folding of the polypeptide chain, is responsible for preventing the B‐to‐A transition; this occurs either by protecting the high‐humidity modified B form against dehydration or by steric interference of this protein probably located in one of the DNA grooves.