Functional properties of the N-terminal region of progesterone receptors and their mechanistic relationship to structure

J Steroid Biochem Mol Biol. 2003 Jun;85(2-5):209-19. doi: 10.1016/s0960-0760(03)00197-3.


Progesterone receptors (PR) are present in two isoforms, PR-A and PR-B. The B-upstream segment (BUS) of PR-B is a 164 amino acid N-terminal extension that is missing in PR-A and is responsible for the functional differences reported between the two isoforms. BUS contains an activation function (AF3) which is defined by a core domain between residues 54-154 whose activity is dependent upon a single Trp residue and two LXXLL motifs. We have also identified sites both within and outside of BUS that repress the strong synergism between AF3 and AF1 in the N-terminal region and AF2 in the hormone binding domain. One of these repressor sites is a consensus binding motif for the small ubiquitin-like modifier protein, SUMO-1 (387IKEE). The DNA binding domain (DBD) structure is also important for function. When BUS is linked to the glucocorticoid receptor DBD, AF3 activity is substantially attenuated, suggesting that binding to a DNA response element results in allosteric communication between the DBD and N-terminal functional regions. Lastly, biochemical and biophysical analyses of highly purified PR-B and PR-A N-terminal regions reveal that they are unstructured unless the DBD is present. Thus, the DBD stabilizes N-terminal structure. We propose a model in which the DBD through DNA binding, and BUS through protein-protein interactions, stabilize active receptor conformers within an ensemble distribution of active and inactive conformational states. This would explain why PR-B are stronger transactivators than PR-A.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • COS Cells
  • Chlorocebus aethiops
  • HeLa Cells
  • Humans
  • Molecular Sequence Data
  • Mutagenesis
  • Peptide Fragments / chemistry
  • Protein Isoforms / chemistry
  • Protein Isoforms / physiology
  • Receptors, Progesterone / chemistry*
  • Receptors, Progesterone / genetics
  • Receptors, Progesterone / physiology*
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Transcription, Genetic
  • Transfection


  • Peptide Fragments
  • Protein Isoforms
  • Receptors, Progesterone
  • Recombinant Proteins
  • progesterone receptor A
  • progesterone receptor B