Distinction and similarity in the structure of histones H1 and H5 as indicated by 13C nuclear-magnetic-resonance spectroscopy

The 13C nuclear magnetic resonance studies have been carried out on histones H1 and H5, by focusing our interest on possible formation of specific salt bridges between acidic and basic amino acid residues in the proteins and also on the structural difference between the two proteins. The 13C chemical shift and pKa values of the carboxyl group of glutamic acid residues in the histones coincided with those of free glutamic acid. Based on this result and another experiment using completely modified lysine residues in the histones, no evidence for a specific interaction between acidic and basic residues has been found. It has also been shown that the pH-effects of aliphatic and aromatic resonances are quite different between H1 and H5, suggesting that the globular domain of H5 is more stable than that of H1. The correlation time (1.5 ns) for the alpha-carbons of H5 estimated from 13C nuclear Overhauser enhancement was twice as long as that of H1 (0.9 ns), indicating that the backbone in the N-terminal and C-terminal domains of H5 is less mobile than that of H1.