Structural investigations of chromatin core protein by nuclear magnetic resonance

Abstract

A complex derived from [calf thymus or chicken erythrocyte] chromatin containing 1 molecule of each of histones H2A, H2B, H3 and H4, termed core protein, was studied by 13C and 1H NMR. 13C line widths, when analyzed and compared with those of native and thermally unfolded representative globular proteins, showed that regions of the core protein passes considerable mobility. Studies of C.alpha. and C.beta. line widths, and C.alpha. spin-spin relaxation times, show that this mobility arises from sections of random-coil polypeptide. It is argued that these regions are N-terminal tails, attached to C-terminal globular polypeptides. The 270-MHz1H NMR spectrum shows numerous ring current shifted resonances, indicating that the C-terminal globular domain has a precise tertiary structure. The globular domain most likely forms the histone core of the chromatin monomer particle while the basic tails probably wind around the grooves of the double helix, enabling the basic side chains to interact with the DNA phosphate groups. Some biological implications of this model are considered.