Malignant cancer is one of the leading causes of death in modern world. In order to devise new therapies the mechanisms of cancer (and metastasis) development are intensively studied. One target of these studies is the hedgehog (Hh) signalling pathway that has a central role in development and is essential for the maintenance of certain tissues in adults. Damage to this pathway can cause severe birth defects, a number of common cancers, sterility and baldness. All the signalling in this pathway is mediated by Smoothened, a seven-pass transmembrane receptor that belongs to a large superfamily of ~800 signalling proteins - G-protein-coupled receptors (GPCRs). Understanding of Hh signal transduction will be crucial for identifying potential drug targets and development of new therapies. The central role of Smo in Hh pathway makes it an attractive target for drug design. Despite clinical relevance of GPCRs (they represent more than 50% current drug targets), only couple of high-resolution structures of these receptors has been obtained. The reason is that GPCRs occur naturally at low levels and heterologous expression of such complex proteins as well as their purification in intact form and required amount is a difficult task. However, some progress has been recently achieved in the field. The aim of this project is to overexpress, label and produce intracellular domains of human Smo and its cancer-relevant mutants in Escherichia coli expression system. Purified Smo proteins will be used in functional and structural studies essential to elucidate its functions and interactions with other proteins, activators and inhibitors in Hedgehog pathway.