Allosteric modulation of the G protein-coupled US28 receptor of human cytomegalovirus: are the small-weight inverse agonist of US28 'camouflaged' agonists?

The highly constitutively active G protein-coupled receptor US28 of human cytomegalovirus (HCMV) is thought to camouflage agonism by mediating constitutive endocytosis. With the use of the US28Δ300 mutant, which is largely devoid of constitutive internalization, I have demonstrated that the coupling of the receptor to its downstream signaling partners is responsible for the inverse agonism to agonism efficacy switch in some small-weight ligands of US28.