Ligand binding site interaction in adenosine cyclic 3',5'-monophosphate dependent protein kinase catalytic subunit: circular dichroic evidence for intramolecular transmission of conformational change.

Blue Dextran has been shown to interact specifically with the nucleotide binding site of the catalytic subunit of cAMP-dependent protein kinase. By observing changes in the induced dichroism associated with the absorbance of the bound chromophore, one can monitor conformational changes in the immediate vicinity of the ATP binding site. With this technique, it has been possible to demonstrate that attachment of ligand at the protein substrate binding site of the enzyme results in a conformational change at the ATP binding site. This alteration takes place in at least two steps, one of which appears to be dependent on the presence of a phosphorylatable hydroxyl group on the substrate and the other being triggered by the "basic subsite" (usually one or more arginine residues) to the N-terminal side of the target serine or threonine. Competition experiments suggest that the change induced results in closure over the substrate protein after the initial electrostatic binding; the movement initiated by the presence of a serine hydroxyl group may also involve interaction with a tyrosine residue at the surface of the ATP binding site.