The nuclear receptor corepressor (N-CoR) contains three isoleucine motifs (I/LXXII) that serve as receptor interaction domains (IDs).
Unliganded thyroid hormone receptors (TRs) repress transcription through recruitment of corepressors, including nuclear receptor corepressor (N-CoR). We find that N-CoR contains three interaction domains (IDs) that bind to TR, rather than the previously reported two. The hitherto unrecognized ID (ID3) serves as a fully functional TR binding site, both in vivo and in vitro, and may be the most important for TR binding. Each ID motif contains a conserved hydrophobic core (I/LXXII) that resembles the hydrophobic core of nuclear receptor boxes (LXXLL), which mediates p160 coactivator binding to liganded nuclear receptors. Although the integrity of the I/LXXII motif is required for ID function, substitution of ID isoleucines with leucines did not allow ID peptides to bind to liganded TR, and substitution of NR box leucines with isoleucines did not allow NR box peptides to bind unliganded TR. This indicates that the binding preferences of N-CoR for unliganded TR and p160s for liganded TR are not dictated solely by the identity of conserved hydrophobic residues within their TR binding motifs. Examination of sequence conservation between IDs, and mutational analysis of individual IDs, suggests that they are comprised of the central hydrophobic core and distinct adjacent sequences that may make unique contacts with the TR surface. Accordingly, a hybrid peptide that contains distinct adjacent sequences from ID3 and ID1 shows enhanced binding to TR.
Webb
P
P
Metabolic Research Unit, University of California School of Medicine, San Francisco 94143-0540, USA.
Anderson
C M
CM
Valentine
C
C
Nguyen
P
P
Marimuthu
A
A
West
B L
BL
Baxter
J D
JD
Kushner
P J
PJ
D020816:Amino Acid Motifs; D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo; D007532:Isoleucine / Q000378:metabolism*; D046911:Macromolecular Substances; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D056971:Nuclear Receptor Co-Repressor 1; D009842:Oligopeptides / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011988:Receptors, Thyroid Hormone / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D020798:Two-Hybrid System Techniques
D046911:Macromolecular Substances; D009687:Nuclear Proteins; D056971:Nuclear Receptor Co-Repressor 1; D009842:Oligopeptides; D011988:Receptors, Thyroid Hormone; D012097:Repressor Proteins; D007532:Isoleucine