Low resolution structures of the retinoid X receptor DNA-binding and ligand-binding domains revealed by synchrotron X-ray solution scattering.
Nuclear receptors are ligand-inducible transcription factors that share structurally related DNA-binding (DBD) and ligand-binding (LBD) domains. Biochemical and structural studies have revealed the modular nature of DBD and LBD. Nevertheless, the domains function in concert in vivo. While high-resolution crystal structures of nuclear receptor DBDs and LBDs are available, there are no x-ray structural studies of nuclear receptor proteins containing multiple domains. We report the solution structures of the human retinoid X receptor DBD-LBD (hRXRalphaDeltaAB) region. We obtained ab initio shapes of hRXRalphaDeltaAB dimer and tetramer to 3.3 and 1.7 nm resolutions, respectively, and established the position and orientation of the DBD and LBD by fitting atomic coordinates of hRXRalpha DBD and LBD. The dimer is U-shaped with DBDs spaced at approximately 2 nm in a head to head orientation forming an angle of about 10 degrees with respect to each other and with an extensive interface area provided by the LBD. The tetramer is a more elongated X-shaped molecule formed by two dimers in head to head arrangement in which the DBDs are extended from the structure and spaced at about 6 nm. The close proximity of DBDs in dimers may facilitate homodimer formation on DNA; however, for the homodimer to bind to a DNA element containing two directly repeated half-sites, one of the DBDs would need to rotate with respect to the other element. By contrast, the separation of DBDs in the tetramers may account for their decreased ability to recognize DNA.
Fischer
Hannes
H
Instituto de Fisica de São Carlos, Universidade de São Paulo, Av. Trabalhador São Carlense, 400 São Carlos, SP, Brazil 13560-970.
Dias
Sandra M G
SM
Santos
Maria A M
MA
Alves
Adriana C
AC
Zanchin
Nilson
N
Craievich
Aldo F
AF
Apriletti
James W
JW
Baxter
John D
JD
Webb
Paul
P
Neves
Francisco A R
FA
Ribeiro
Ralff C J
RC
Polikarpov
Igor
I
D001665:Binding Sites; D004247:DNA / Q000378:metabolism*; D019281:Dimerization; D008024:Ligands; D018168:Receptors, Retinoic Acid / Q000737:chemistry* / Q000378:metabolism; D047488:Retinoid X Receptors; D012542:Scattering, Radiation; D012996:Solutions; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism; D014965:X-Rays
D008024:Ligands; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D012996:Solutions; D014157:Transcription Factors; D004247:DNA