Effect of tyrosine isomers on the insulin signaling

Our cooperation manifests in the joint action of a peptide chemist, a biochemist and a physician, targeting the research of the damage of proteins due to non-physiological tyrosine isomers starting by chemical modeling through the processes of subcellular and cellular damage and ending by the clinical entities. In patients with subclinical or clinically manifest inflammation, this inflammation induces intracellular oxidative stress and a production of hydroxyl free radical. Hydroxyl free radical hydroxylating phenylalanine forms non-physiological ortho- and meta-tyrosine. These tyrosine isomers incorporate into the proteins leading to the damage of signaling pathways, which is an important player in all pathological processes and in various clinical entities as a causative or additive factor. Basically, this could lead to a disorder of cell regulation and clinically involves kidney, heart, vascular, inflammatory, and cancerous diseases and their possible new therapies. Moreover, supplementation of the physiological para-tyrosine in some diseases could be beneficial being competitive antagonist of the incorporation of non-physiological tyrosine isomers. Our goal is to model these processes above, as one could see in the figure below.

The targeted signaling polypeptide fragment of IRS-1 will be chemically synthesized. We need 6 different types of polypeptide: the physiological para-tyrosine and its phosphorylated form, ortho-tyrosine and its phosphorylated form, meta-tyrosine and its phosphorylated form. In the next step we will examine the binding of insulin receptor to the non-phosphorylated form of these polypeptides and the consequent phosphorylation of them. Following, the binding and the dephosphorylation of the phosphorylated polypetides (para-, ortho-, meta-tyrosine) by the protein tyrosine phosphatase-1B will be examined. In the signaling pathway the next step is the binding of the p85 segment of PI3K to the phosphorylated IRS-1, that is why we will study this binding in cases of phosphorylated para-, ortho-, and meta-tyrosine containing polypeptide. Parallel, we will culture fat cells on three different types of mediums, containing para-, meta-, and ortho-tyrosine studying the activating phosphorylation of IRS-1 and measuring the incorporation of the non-physiological tyrosines. As a next step, we will search in cultured kidney podocytes the possible immunofluorescent changes in the cell markers due to ortho-, meta-tyrosines, and these changes will be searched in the kidney biopsy specimens of human diseases.

Gábor Tóth - Attila Reményi - István Wittmann