Structure of a complex of catabolite gene activator protein and cyclic AMP refined at 2.5 Å resolution

Abstract

The structure of a dimer of the Escherichia coli catabolite gene activator protein has been refined at 2.5 Å resolution to a crystallographic R-factor of 20.7% starting with coordinates fitted to the map at 2.9 Å resolution. The two subunits are in different conformations and each contains one bound molecule of the allosteric activator, cyclic AMP. The amino-terminal domain is linked to the smaller carboxy-terminal domain by a nine-residue hinge region that exists in different conformations in the two subunits, giving rise to approximately a 30 ° rotation between the positions of the small domains relative to the larger domains. The amino-terminal domain contains an antiparallel β-roll structure in which the interstrand hydrogen bonding is well-determined. The β-roll can be described as a long antiparallel β-ribbon that folds into a right-handed supercoil and forms part of the cyclic AMP binding site. Each cyclic AMP molecule is in an anti conformation and has ionic and hydrogen bond interactions with both subunits.