Ludmilla Ferreira Cardoso1, Maria Clara de Carvalho Melo2, Mirian Hideco Takahashi3, Alessandro Silva Nascimento4, Maria Izabel Chiamolera2, Léa Maria Zanini Maciel5. 1. Department of Internal Medicine, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil. 2. Laboratory of Molecular and Translational Endocrinology, Department of Medicine, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP, Brazil. 3. Department of Medicine, Universidade Estadual de Maringá, Maringá, PR, Brazil. 4. São Carlos Institute of Physics, University of São Paulo, São Carlos, SP, Brazil. 5. Department of Internal Medicine, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil. lmzmacie@fmrp.usp.br.
Abstract
PURPOSE: Among the inheritable forms of impaired sensitivity to thyroid hormone, resistance to thyroid hormone (RTH) due to mutations in the thyroid hormone receptor beta gene (THRB) is the first and best known described defect, revealing a wide phenotypic variability with an incompletely understood physiopathology. The objective of this study was to evaluate two novel mutations in THRB, N331H and L346R, in an attempt to provide a rational understanding of the harmful effects caused by them. METHODS: The mutations of two patients with RTHβ were reproduced for analysis of gene transactivation by dual-luciferase reporter assay, and for molecular modeling for crystallography-based structural assessment. Serum measurements of TSH and FT4 were performed to compare the thyrotrophic resistance to thyroid hormone between RTHβ patients and controls. RESULTS: Both mutants showed impaired gene transactivation, with greater damage in L346R. Molecular modeling suggested that the damage occurring in N331H is primarily due to reduced strength of the hydrogen bonds that stabilize T3 in its ligand-binding cavity (LBC), whereas in L346R, the damage is more marked and is mainly due to changes in hydrophobicity and molecular volume inside the LBC. Hormonal dosages indicated that the L346R mutant exhibited greater thyrotrophic resistance than N331H. CONCLUSIONS: This study provides a rational understanding of the effects of mutations, indicating deleterious structural changes in the LBC in both THR, and discloses that not only the position of the mutation but, notably, the nature of the amino acid exchange, has a cardinal role in the functional damage of the receptor.
PURPOSE: Among the inheritable forms of impaired sensitivity to thyroid hormone, resistance to thyroid hormone (RTH) due to mutations in the thyroid hormone receptor beta gene (THRB) is the first and best known described defect, revealing a wide phenotypic variability with an incompletely understood physiopathology. The objective of this study was to evaluate two novel mutations in THRB, N331H and L346R, in an attempt to provide a rational understanding of the harmful effects caused by them. METHODS: The mutations of two patients with RTHβ were reproduced for analysis of gene transactivation by dual-luciferase reporter assay, and for molecular modeling for crystallography-based structural assessment. Serum measurements of TSH and FT4 were performed to compare the thyrotrophic resistance to thyroid hormone between RTHβ patients and controls. RESULTS: Both mutants showed impaired gene transactivation, with greater damage in L346R. Molecular modeling suggested that the damage occurring in N331H is primarily due to reduced strength of the hydrogen bonds that stabilize T3 in its ligand-binding cavity (LBC), whereas in L346R, the damage is more marked and is mainly due to changes in hydrophobicity and molecular volume inside the LBC. Hormonal dosages indicated that the L346R mutant exhibited greater thyrotrophic resistance than N331H. CONCLUSIONS: This study provides a rational understanding of the effects of mutations, indicating deleterious structural changes in the LBC in both THR, and discloses that not only the position of the mutation but, notably, the nature of the amino acid exchange, has a cardinal role in the functional damage of the receptor.
Entities:
Keywords:
Crystallography; L346R THRB mutation; N331H THRB mutation; Resistance to thyroid hormone beta; Structural analysis; Thyrotroph T4 resistance index
Authors: M E Geffner; F Su; N S Ross; J M Hershman; C Van Dop; J B Menke; E Hao; R K Stanzak; T Eaton; H H Samuels Journal: J Clin Invest Date: 1993-02 Impact factor: 14.808