Phosphorylation of lysosomal enzymes
Abstract
Proteins, lipids and carbohydrates in any organism are subject to a certain degree of turnover ¿ which means a cycle of biosynthesis and degradation occurs. Also an animal¿s own serum proteins, as well as foreign proteins or organisms in the bloodstream, are internalised by cells and often degraded. In animals the relevant compartment of the cell where degradation takes place is called the lysosome. The various proteases, glycosidases and other catabolic enzymes necessary for this degradation must carry a special marker (mannose-6-phosphate) in order to be correctly located within to the lysosome. The lack of this marker leads to the enzymes not being directed to the lysosome and to a build-up of undegraded protein, lipid or carbohydrate. The resulting overfilling of the lysosome leads to the cell being malformed. Clinically the absence of correctly-localised lysosomal enzymes results in various lysosomal storage disorders. The mannose-6-phosphate marker is attached to the enzymes in a two-stage process by which first N-acetylglucosamine-1-phosphotransferase and then a N-acetylglucosaminidase act on the mannose-containing carbohydrate side chain of the lysosomal enzyme resulting in the appearance of mannose-6-phosphate as a terminal grouping. The necessary enzymes have been purified by others, but the gene sequence of the transferase has not been reported. In order to be able to examine the biosynthesis of mannose-6-phosphate further, a candidate gene will be expressed and the encoded recombinant enzyme prepared. This should then open the way to prepare properly phosphorylated lysosomal enzymes which could be used in enzyme replacement therapy. Knowledge of which gene is exactly involved should also help in molecular diagnosis of lysosomal storage disorders.
Project staff
Iain B.H. Wilson
ao.Univ.Prof. Dr.phil. Iain B.H. Wilson
iain.wilson@boku.ac.at
Tel: +43 1 47654-77216, 77217
Project Leader
01.12.2003 - 31.12.2004