engleski

Homology Modeling of Smoothened Protein and Structural Analysis of Its Activating Mutations

Smoothened protein, encoded by the SMO gene of the Hedgehog (Hh) signaling pathway, belongs to class F (Frizzled/Smoothened) of G protein-coupled receptors (GPCRs), superfamily of integral membrane proteins encoded by about 5% of human genes. Although tertiary structural information is crucial for function annotation and potential drug design, the three dimensional structure of Smoothened protein has not been experimentally determined yet. Because of that, homology modeling is a helpful technique to reveal its tertiary structure. In inactive Hh pathway, Smoothened is repressed by Protein patched homolog 1 (Ptch) until ligand Sonic hedgehog homolog (Shh) binds to Ptch. Some Smoothened amino acid changes act as activating missense mutations (e.g. Trp535Leu and Arg562Gln) that can lead to unregulated activation of the Hedgehog signaling pathway and therefore to cancer, what was shown in sporadic basal-cell carcinoma. We used de novo protein structure prediction and comparative modeling by using known X-ray structures of GPCRs as templates (rhodopsin, β1-adrenergic receptor, Frizzled) to model tertiary structure of Smoothened. The best predicted 3D model was then used to investigate how polymorphisms and known activating mutations, found in basal cell carcinoma, could affect the structure and stability of the protein. This modeled three dimensional structure of Smoothened protein could be further used to identify the possible mechanism of Smoothened inhibition by plant-derived teratogen cyclopamine and then virtual screening of compound libraries can be performed to find new potential antagonists of Smoothened protein, which could be used as therapeutic agents.

Smoothened ; GPCR ; comparartive modeling ; 3D structure ; mutations

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