Multidomain integration in the structure of the HNF-4α nuclear receptor complex

The hepatocyte nuclear factor 4 alpha (HNF-4 alpha; also known as NR2A1) is a member of the nuclear receptor (NR) family of transcription factors, which have conserved DNA-binding domains and ligand-binding domains(1,2). HNF-4 alpha is the most abundant DNA-binding protein in the liver, where some 40% of the actively transcribed genes have a HNF-4 alpha response element(1,3,4). These regulated genes are largely involved in the hepatic gluconeogenic program and lipid metabolism(3,5,6). In the pancreas HNF-4 alpha is also a master regulator, controlling an estimated 11% of islet genes(7). HNF-4 alpha protein mutations are linked to maturity-onset diabetes of the young, type 1 (MODY1) and hyperinsulinaemic hypoglycaemia(8-11). Previous structural analyses of NRs, although productive in elucidating the structure of individual domains, have lagged behind in revealing the connectivity patterns of NR domains. Here we describe the 2.9 angstrom crystal structure of the multidomain human HNF-4 alpha homodimer bound to its DNA response element and coactivatorderived peptides. A convergence zone connects multiple receptor domains in an asymmetric fashion, joining distinct elements from each monomer. An arginine target of PRMT1 methylation protrudes directly into this convergence zone and sustains its integrity. A serine target of protein kinase C is also responsible for maintaining domain-domain interactions. These post-translational modifications lead to changes in DNA binding by communicating through the tightly connected surfaces of the quaternary fold. We find that some MODY1 mutations, positioned on the ligand-binding domain and hinge regions of the receptor, compromise DNA binding at a distance by communicating through the interjunctional surfaces of the complex. The overall domain representation of the HNF-4 alpha homodimer is different from that of the PPAR-gamma-RXR-alpha heterodimer, even when both NR complexes are assembled on the same DNA element. Our findings suggest that unique quaternary folds and interdomain connections in NRs could be exploited by small-molecule allosteric modulators that affect distal functions in these polypeptides.