Lefebvre B, Mouchon A, Formstecher P, Lefebvre P
INSERM U 459, Laboratoire de Biochimie Structurale, Faculté de Médecine Henri Warembourg, Lille, France.
Mol Cell Endocrinol. 1998 Apr 30;139(1-2):161-9. doi: 10.1016/s0303-7207(98)00065-3.
Retinoids regulate key cellular processes through their binding to their cognate nuclear receptors, RARs and RXRs. Synthetic ligands mimic most of their biological effects and alteration of their chemical structure confers selectivity for RAR isotypes alpha, beta or gamma. In this study, we have examined the contribution of a domain (L box) of hRARalpha located at the C-terminus of the ligand binding domain (LBD), between helices H11 and H12, to the ligand binding activity of this receptor. By site-directed mutagenesis, we demonstrate that, in the absence of the ligand-dependent activation domain 2 (AF2-AD), the receptor discriminates between classes of structurally distinct retinoids. This property was lost in the presence of the AF2-AD domain, evidencing major structural transitions in this part of the receptor. We propose that ligand binding occurs in two steps: first, the ligand interacts with the LBD in its opened, holo-receptor conformation in which the L box plays a crucial role in defining the ligand binding repertoire of hRARalpha; secondly, the LBD adopts its closed conformation in which the ligand interacts with the receptor mostly through its carboxylic moiety.
维甲酸通过与它们的同源核受体RARs和RXRs结合来调节关键的细胞过程。合成配体模拟它们的大多数生物学效应，并且其化学结构的改变赋予了对RAR亚型α、β或γ的选择性。在本研究中，我们研究了位于配体结合结构域（LBD）C末端、螺旋H11和H12之间的hRARα的一个结构域（L盒）对该受体配体结合活性的贡献。通过定点诱变，我们证明，在没有配体依赖性激活结构域2（AF2-AD）的情况下，该受体能够区分结构不同的维甲酸类别。在存在AF2-AD结构域的情况下，这一特性丧失，表明该受体这一部分发生了重大的结构转变。我们提出配体结合分两步进行：首先，配体以其开放的全受体构象与LBD相互作用，其中L盒在定义hRARα的配体结合谱中起关键作用；其次，LBD采用其封闭构象，其中配体主要通过其羧基部分与受体相互作用。
