Therapeutic approaches for the correction of misfolding mutations in pterin-dependent enzymes

Many inherited diseases are caused by the enhanced tendency of the mutant variant proteins to misfold and to either undergo proteasomal degradation or deleterious aggregation with plaque formation. For several of these diseases evidence has been accumulat ed that chemical or pharmacologic chaperones (pharmacoperones) rescue the misfolded proteins by stimulating their renaturation in vitro and in vivo. Recent results with several systems show that successful therapeutic intervention includes the stabilizati on of mutant receptors and enzymes by molecules resembling natural agonists or antagonists, as well as cofactors. We have recently successfully elucidated the molecular chaperon-like mechanism by which phenylketonuria patients harboring a subset of phenyl alanine hydroxylase (PAH) mutations show normalization of blood phenylalanine levels upon oral administration of the PAH cofactor tetrahydrobiopterin. Based on this experience, we would like now to develop the basic protein physicochemical aspects of this concept as well as to pursue the search for pharmacoperones with potential in other important diseases associated to malfunction of tetrahydrobiopterin-dependent aromatic amino acid hydroxylases, such as DOPA-responsive dystonias, Parkinsons? disease and psychiatric disorders. In the case of absolute deleterious mutations or dysfunctions which cannot be rescued by pharmacoperones, the enzyme replacement therapy (ERT) approach appears promising. ERT has gained popularity in the treatment of lysosomal sto rage disease and other metabolic diseases, thus circumventing the difficulties with gene therapy. ERT requires the chemical modification and immobilization of the enzymes in order to increase their stability and functionality, as well as to decrease their immunogeneicity. In this project we aim to apply structural and stability determinants from small thermostable bacterial enzymes as leads for further development of protein therapeutics.