title: Communication between the ERRalpha homodimer interface and the PGC-1alpha binding surface via the helix 8-9 loop.
abstract: Although structural studies on the ligand-binding domain (LBD) have established the general mode of nuclear receptor (NR)/coactivator interaction, determinants of binding specificity are only partially understood. The LBD of estrogen receptor-alpha (ERalpha), for example, interacts only with a region of peroxisome proliferator-activated receptor coactivator (PGC)-1alpha, which contains the canonical LXXLL motif (NR box2), whereas the LBD of estrogen-related receptor-alpha (ERRalpha) also binds efficiently an untypical, LXXYL-containing region (NR box3) of PGC-1alpha. Surprisingly, in a previous structural study, the ERalpha LBD has been observed to bind NR box3 of transcriptional intermediary factor (TIF)-2 untypically via LXXYL, whereas the ERRalpha LBD binds this region of TIF-2 only poorly. Here we present a new crystal structure of the ERRalpha LBD in complex with a PGC-1alpha box3 peptide. In this structure, residues N-terminal of the PGC-1alpha LXXYL motif formed contacts with helix 4, the loop connecting helices 8 and 9, and with the C terminus of the ERRalpha LBD. Interaction studies using wild-type and mutant PGC-1alpha and ERRalpha showed that these contacts are functionally relevant and are required for efficient ERRalpha/PGC-1alpha interaction. Furthermore, a structure comparison between ERRalpha and ERalpha and mutation analyses provided evidence that the helix 8-9 loop, which differs significantly in both nuclear receptors, is a major determinant of coactivator binding specificity. Finally, our results revealed that in ERRalpha the helix 8-9 loop allosterically links the LBD homodimer interface with the coactivator cleft, thus providing a plausible explanation for distinct PGC-1alpha binding to ERRalpha monomers and homodimers.
authors.affiliation: Département de Biologie et Génomique Structurales, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France.
authors.forename: Holger
authors.initials: H
authors.lastname: Greschik
authors.forename: Magnus
authors.initials: M
authors.lastname: Althage
authors.forename: Ralf
authors.initials: R
authors.lastname: Flaig
authors.forename: Yoshiteru
authors.initials: Y
authors.lastname: Sato
authors.forename: Virginie
authors.initials: V
authors.lastname: Chavant
authors.forename: Carole
authors.initials: C
authors.lastname: Peluso-Iltis
authors.forename: Laurence
authors.initials: L
authors.lastname: Choulier
authors.forename: Philippe
authors.initials: P
authors.lastname: Cronet
authors.forename: Natacha
authors.initials: N
authors.lastname: Rochel
authors.forename: Roland
authors.initials: R
authors.lastname: Schüle
authors.forename: Per-Erik
authors.initials: PE
authors.lastname: Strömstedt
authors.forename: Dino
authors.initials: D
authors.lastname: Moras
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D019281:Dimerization; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011960:Receptors, Estrogen / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000097983:ERRalpha Estrogen-Related Receptor
chemical_list: D006360:Heat-Shock Proteins; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D011960:Receptors, Estrogen; D014157:Transcription Factors; D000097983:ERRalpha Estrogen-Related Receptor; C486497:PPARGC1A protein, human