Functionally Orthogonal Ligand−Receptor Pairs for the
Selective Regulation of Gene Expression Generated by
Manipulation of Charged Residues at the Ligand−Receptor
Interface of ERα and ERβ
posted on 2002-05-23, 00:00authored byYouheng Shi, John T. Koh
The reengineering of protein-small molecule interfaces represents a powerful tool of chemical
biology. For many applications it is necessary to engineer receptors so that they do not interact with their
endogenous ligands but are highly responsive to designed ligand analogues, which in turn do not interact
with endogenous proteins. The chemical design strategy used to reengineer protein−small molecule
interfaces is particularly challenging for interfaces involving relatively plastic receptor binding sites and
therefore presents a unique challenge in molecular design. In this study we explore the scope and limitations of a new strategy for manipulating polar/charged residues across the ligand receptor interface of
estradiol (E2) and the estrogen receptor (ER). Carboxylate-functionalized E2 analogues can activate
ERα(Glu353→Ala) and ERβ(Glu305→Ala) with very large selectivites, demonstrating that this design strategy
is extendable to other members of the steroid hormone receptor family. Neutral E2 analogues were found
to complement ERα(E353A) with similar potencies but with generally lower selectivities. This suggests
that the high selectivity observed with ligand−receptor pairs generated by exchanging charged residues
across ligand−receptor interfaces is only due in part to their complementary shapes and that appropriate
introduction of charged functionality on the ligand can provide substantial enhancement of selectivity by
decreasing the engineered ligands affinity for the endogenous receptor. Attempts to modify the cationic
residues by complementing Arg394→Ala or Arg394→Glu were not successful.