As of yet, the actual conformational changes that occur are not known,
because the crystal structure of the holoenzyme R2C2 tetramer has not been
solved. However, some of the networking interactions are known.
An example of this interaction is the alpha NH of Glu199. Glu199 is well conserved among the cAMP binding sites seen ( sites A & B, and the binding site in CAP) The alpha NH of Gly 199 hydrogen bonds to the 2'OH of the cAMP, the alpha NH of Glu200 bonds to the OE2 of its own side chain. The alpha NH of Ala202 hydrogen bonds to the equitorial oxygen of the phosphate in cAMP. The alpha NH of Leu203 hydrogen bonds to the alpha carbonyl of Leu201.
The network is shown in the above graphic, and makes it easier to see how cAMP can effect a conformational change. The actual conformational change has not been seen yet, but some idea can be gotten of how the binding of the cyclic AMP transmits a signal throughout the protein.