title: The N-terminal region of human progesterone B-receptors: biophysical and biochemical comparison to A-receptors.
abstract: To understand the basis for functional differences between the two human progesterone receptors (PR), we have carried out a detailed biochemical and biophysical analysis of the N-terminal region of each isoform. Extending our previous work on the A-isoform (Bain, D. L, Franden, M. A., McManaman, J. L., Takimoto, G. S., and Horwitz, K. B. (2000) J. Biol. Chem. 275, 7313-7320), here we present studies on the N-terminal region of the B-isoform (NT-B) and compare its properties to its A-receptor counterpart (NT-A). As seen previously with NT-A, NT-B is quantitatively monomeric in solution, yet undergoes N-terminal-mediated assembly upon DNA binding. Limited proteolysis, microsequencing, and sedimentation analyses indicate that the B-isoform exists in a non-globular, extended conformation very similar to that of NT-A. Additionally, the 164 amino acids unique to the B-isoform (BUS) appear to be in a more extended conformation relative to sequences common to both receptors and do not exist as an independent structural domain. However, sedimentation studies of NT-A and NT-B show differences in the ensemble distribution of their conformational states. We hypothesize that isoform-specific functional differences are not due to structural differences, per se. Rather, the transcriptional element BUS, or possibly other transcription factors, causes a redistribution of the conformational ensemble by stabilizing a more functionally active set of conformations in NT-B.
authors.affiliation: Department of Medicine and The Molecular Biology Program, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA. david.bain@uchsc.edu
authors.forename: D L
authors.initials: DL
authors.lastname: Bain
authors.forename: M A
authors.initials: MA
authors.lastname: Franden
authors.forename: J L
authors.initials: JL
authors.lastname: McManaman
authors.forename: G S
authors.initials: GS
authors.lastname: Takimoto
authors.forename: K B
authors.initials: KB
authors.lastname: Horwitz
mesh_terms: D006801:Humans; D007700:Kinetics; D011487:Protein Conformation; D011980:Receptors, Progesterone / Q000737:chemistry* / Q000378:metabolism; D020218:Response Elements; D014158:Transcription, Genetic; D014461:Ultracentrifugation
chemical_list: D011980:Receptors, Progesterone; C101118:progesterone receptor A; C097314:progesterone receptor B