Leibniz-Institut für Molekulare Pharmakologie, 13125 Berlin, Germany.
Biochem Soc Trans. 2013 Feb 1;41(1):213-7. doi: 10.1042/BST20120319.
The TSHR (thyrotropin receptor) is activated endogenously by the large hormone thyrotropin and activated pathologically by auto-antibodies. Both activate and bind at the extracellular domain. Recently, SMLs (small-molecule ligands) have been identified, which bind in an allosteric binding pocket within the transmembrane domain. Modelling driven site-directed mutagenesis of amino acids lining this pocket led to the delineation of activation and inactivation sensitive residues. Modified residues showing CAMs (constitutively activating mutations) indicate signalling-sensitive positions and mark potential trigger points for agonists. Silencing mutations lead to an impairment of basal activity and mark contact points for antagonists. Mapping these residues on to a structural model of TSHR indicates locations where an SML may switch the receptor to an inactive or active conformation. In the present article, we report the effects of SMLs on these signalling-sensitive amino acids at the TSHR. Surprisingly, the antagonistic effect of SML compound 52 was reversed to an agonistic effect, when tested at the CAM Y667A. Switching agonism to antagonism and the reverse by changing either SMLs or residues covering the binding pocket provides detailed knowledge about discriminative pharmacophores. It prepares the basis for rational optimization of new high-affinity antagonists to interfere with the pathogenic activation of the TSHR.
促甲状腺激素受体（TSHR）可被内源的大激素促甲状腺激素激活，也可被自身抗体病理性激活。这两种激活方式都发生在细胞外结构域。最近，已鉴定出小分子配体（SMLs），它们在跨膜结构域的变构结合口袋中结合。基于此口袋中排列的氨基酸的建模定点突变导致了对激活和失活敏感残基的描述。表现出 CAM（组成性激活突变）的修饰残基表明了信号敏感位置，并标记了潜在的激动剂触发点。沉默突变导致基础活性受损，并标记了拮抗剂的接触点。将这些残基映射到 TSHR 的结构模型上，表明了 SML 可能将受体转换为非活性或活性构象的位置。在本文中，我们报告了 SML 对 TSHR 上这些信号敏感氨基酸的影响。令人惊讶的是，当在 Y667A CAM 上测试时，SML 化合物 52 的拮抗作用被逆转为激动作用。通过改变 SML 或覆盖结合口袋的残基，将激动作用切换为拮抗作用和相反作用，提供了关于区分药效团的详细知识。这为理性优化新的高亲和力拮抗剂以干扰 TSHR 的致病激活奠定了基础。
