Structural studies of the thyroid receptor (TR) and homology modeling of the thyroxine binding globulin (TBG) / Estudos estruturais do receptor do hormônio tireoidiano (hTR) e modelagem por homologia da globulina de ligação à tiroxina (TBG)

AUTOR(ES)

Lucas Bleicher

DATA DE PUBLICAÇÃO

2005

RESUMO

The thyroid hormones are involved in various regulatory effects, on diverse organs. Their fluctuations on the body are related to clinical scenarios of great relevance. This work deals with the study of two proteins which are directly related to the regulatory system associated to these hormones. The first one is the thyroxine-binding globulin (TBG), responsible for the transport of a large part of the thyroid hormones in serum, and whose variations are related to misinterpretation of thyroid function tests. The second protein is the thyroid receptor (TR), responsible for the mediation of the thyroid hormone regulatory effects . the transcriptional activity being related to ligand binding to one of the protein domains. The wild-type TBG and three mutants discovered in Brazil were studied by the computational technique known as homology modeling. The purpose of this investigation was to relate protein unviability to structural aspects. It was proposed that, for two mutants, the unviability was related to the impossibility of secondary structure formation as needed to form the native folding, while the third mutant the cause could be the formation of an incorrect folding due to possible interactions involving a cysteine residue created by the mutation and other nearby cysteine residues. The thyroid receptor was studied in the light of the x-ray structures of the two isoforms of the protein (hTR α and hTRβ) bound to GC-1, a synthesized compound which resembles the thyroid hormones. This ligand binds preferably the isoform, a feature that may have interesting pharmacological applications. The comparative analysis of GC-1 binding to the two isoforms allowed the construction of a structural basis of its -selectivity property, which is due to considerable differences in the binding modes for the two isoforms. This involves two different configurations of ligand and protein conformations for the isoform - on one of them, the ligand docks to the molecule the same way it docks to hTRβ, while on the second configuration it loses one direct interaction to the protein, explaining its lower affinity to hTR α when compared to hTRβ. The -selectivity mechanism for this compound is related to a specific oxygen atom which doesn?t exist on the receptor endogenous ligand, providing useful information for the development of new compounds.

ASSUNTO(S)

cristalografia de proteínas modelagem por homologia homology modeling gc-1 cg-1 tiromiméticos thyroid hormone thyromimetics hormônio tireoidiano protein crystallography

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