A Nuclear‐Magnetic‐Resonance Study of the Globular Structure of the H1 Histone

The globular structure of the H1 histone has been studied by 1 H NMR, as an aid to elucidating its mode of action, and also as a model small protein molecule for investigating the capabilities of NMR for gaining information about the tertiary folding when the structure has not been determined by other techniques. Guanidylation of the lysine residues does not effect the capability of the peptide chain to fold into the native globular structure, suggesting that the lysine residues are on the surface of the structure. Partial assignment has been made of some of the ring‐current‐shifted resonances (i.e. resonances from methyl groups of apolar residues which are shifted by their proximity to the magnetic fields of aromatic rings) by a combination of spin‐decoupling experiments and theoretical ring‐current‐shift stimulations. Substitution of the tyrosine residue of histone H1 considerably weakens the globular structure, and observation of specific changes in the perturbed methyl region of the spectra on substitution indicates the aromatic residues giving rise to ring‐current perturbation of specific peaks in the spectrum. Interproton Overhauser effects are demonstrated, arising from throughspace dipole interaction between protons of the aromatic residues and methyl residues, the resonances of which are perturbed by close proximity to the aromatic rings. The results of these experiments confirm the assignments made from the results of the tyrosine modification experiments.