Direct structure refinement of high molecular weight proteins against residual dipolar couplings and carbonyl chemical shift changes upon alignment: an application to maltose binding protein

The global fold of maltose binding protein in complex with beta -cyclodextr in has been determined using a CNS-based torsion angle molecular dynamics p rotocol involving direct refinement against dipolar couplings and carbonyl chemical shift changes that occur upon alignment. The shift changes have be en included as structural restraints using a new module, CANI, that has bee n incorporated into CNS. Force constants and timesteps have been determined that are particularly effective in structure refinement applications invol ving high molecular weight proteins with small to moderate numbers of NOE r estraints. Solution structures of the N- and C-domains of MBP calculated wi th this new protocol are within similar to 2 Angstrom of the X-ray conforma tion.