4 MONOCLONAL-ANTIBODIES INHIBIT THE RECOGNITION OF ARYLSULFATASE-A BYTHE LYSOSOMAL-ENZYME PHOSPHOTRANSFERASE

The critical step in the sorting of lysosomal enzymes is their recogni tion by a phosphotransferase in the Golgi apparatus. The topogenic seq uences responsible for the recognition by this enzyme have so far only been defined for the lysosomal protease cathepsin D. We have generate d four monoclonal antibodies directed against lysosomal arylsulphatase A (ASA). These antibodies inhibit the recognition of ASA by the phosp hotransferase in vitro and thus define a region of topogenic sequences in the ASA polypeptide. The antibodies do not interfere with the enzy mic activity nor with pH-dependent dimerization of ASA. The epitopes r ecognized by the antibodies have been located in the second quarter of the ASA polypeptide using chimeric mouse-human ASB molecules. Three o f the monoclonal antibodies bind to identical or closely adjacent epit opes, which are formed by the interaction bf amino acid residues 165-1 84 and 202-240. The fourth antibody recognizes a different epitope wit hin amino acids 256-265.