Structural and biochemical basis for selective repression of the orphan nuclear receptor liver receptor homolog 1 by small heterodimer partner

doi:10.1073/pnas.0501204102

Structural and biochemical basis for selective repression of the orphan nuclear receptor liver receptor homolog 1 by small heterodimer partner

^*Laboratory of Structural Sciences, Van Andel Research Institute, 333 Bostwick Avenue, Grand Rapids, MI 49503; and ^†Departments of Molecular Biology and Pharmacology, University of Texas Southwestern Medical School, 5323 Harry Hines Boulevard, Dallas, TX 75235

Edited by Jan-Åke Gustafsson, Karolinska Institute, Huddinge, Sweden (received for review February 11, 2005)

Abstract

The functional interaction between the orphan nuclear receptors small heterodimer partner (SHP) and liver receptor homolog 1 (LRH-1), where SHP binds to LRH-1 and represses its constitutive transcriptional activity, is crucial for regulating genes involved in cholesterol homeostasis. Here, we report structural and biochemical analyses of the LRH-1/SHP interaction. The crystal structure and modeling studies of the LRH-1 ligand-binding domain bound to either of the two LXXLL-related motifs of SHP show that the receptor undergoes conformational changes to accommodate the SHP docking and reveal key residues that determine the potency and selectivity of SHP binding. Through a combination of mutagenesis and binding studies, we demonstrate that only the second SHP LXXLL motif is required for repressing LRH-1, and this motif displays a strong preference for binding to LRH-1 over the closely related receptor steroidogeneic factor 1 (SF-1). Structural comparisons indicate that this binding selectivity is determined by residues flanking the core LXXLL motifs. These results establish a structural model for understanding how SHP interacts with LRH-1 to regulate cholesterol homeostasis and provide new insights into how nuclear receptor/coregulator selectivity is achieved.

Footnotes

↵ ‡ To whom correspondence should be addressed. E-mail: eric.xu{at}vai.org.
Author contributions: Y.L., M.C., S.A.K., and H.E.X. designed research; Y.L., M.C., K.S., A.K., J.D., S.A.K., and H.E.X. performed research; Y.L., M.C., K.S., A.K., J.D., S.A.K., and H.E.X. analyzed data; and S.A.K. and H.E.X. wrote the paper.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: LRH-1, liver receptor homolog 1; SF-1, steroidogeneic factor 1; LBD, ligand-binding domain; SHP, small heterodimer partner; PPAR, peroxisome proliferator-activated receptor; SRC, steroid receptor coactivator.
Data deposition: The atomic coordinates and structure factors have been deposited in the Protein Data Bank, www.pdb.org [PDB ID codes 1ZH7 (LRH-1/SHP ID1 binary complex) and 1ZGY (PPARγ/rosiglitazone/SHP ID2 ternary complex)].
Freely available online through the PNAS open access option.