A study of the interactions between residues in the C-terminal half of calmodulin by one and two-dimensional NMR methods and computer modelling.

Assignments of the six sets of aromatic ring protons and four high-field-shifted methyl group protons of the C-terminal fragment of calmodulin, residues 78-148, was achieved by a combination of one and two-dimensional NMR spectroscopic methods. A full spectral analysis of the aromatic region in terms of chemical shifts and scalar coupling constants was achieved and confirmed by spectral simulation. A three-dimensional structural model of the C-terminal fragment was constructed by interactive computer graphics techniques and combined with nuclear Overhauser enhancements to propose sequence assignments for all aromatic and high-field-shifted methyl groups. This computer-generated three-dimensional model was generally supported by the fact that it qualitatively accounted for many of the ring-current-shifted proton resonances and the intraresidue and interresidue nuclear Overhauser enhancements.