Large reductions in affinity (>150-fold) for all mutants and all catecholamine ligands, except for the smaller decrease (7-fold) in affinity for dopamine at the D4-S5.43A mutant.

Large reductions in potency for dopamine at all mutants (>40-fold) and large reductions in dopamine efficacy for all mutants except the D4-S5.43A mutant.

Complete loss of efficacy for norepinephrine for all mutants.

Relatively small changes in the affinity (<8-fold) and no significant changes in efficacy of noncatechol agonists.

Relatively small changes in antagonist affinity (<7-fold).

No significant change in noncatechol-like antagonist function. However, Ro10-4548, which contains a catechol-like moiety capable of H-bonding interactions with the conserved TM5 serine side chain, had antagonist properties for the wild-type receptor, but agonist properties for the D4-S5.43A mutant.

Experimental findings support our docking results indicating that, in D4 constructs where the catechol and catechol-like ligands demonstrate significant efficacy, a binding mode is populated where the catechol or catechol-like moiety is accommodated deep in the cleft and H-bonds with the side chains of S5.42 and S5.46.

With respect to catechol agonist interactions, the D4 subtype of dopamine receptor appears to be more similar to the D1 subtype than the D2 and D3 subtypes.