Characterization of a point mutation in aspartylglucosaminidase gene: evidence for a readthrough of a translational stop codon

Abstract

We have identified a novel aspartylglucosaminuria (AGU) mutation In the second exon of the aspartyl-glucosaminldase (AGA) gene resulting In a lysosomal storage disease In a Puerto Rican pedigree. This T₁₉₂→A transverslon causes replacement of Cys₆₄ with a premature translatlonal stop codon and the patients' flbroblasts exhibit dramatically decreased steady-state levels of AGA mRNA. Immunofluorescence analysis and analysis of immunopreclpltated metabolically labelled AGA polypeptides from patient fibroblasts unexpectedly revealed traces of normally sized inactive AGA precursor polypeptide Instead of the predicted short polypeptide of 40 amlno acids, thus demonstrating readthrough due to suppression of the premature translational stop codon. The translated AGA precursor is not processed further and remains Inactive. The Cys₆₄ substitution evidently disturbs the folding of the nascent polypeptide in the endoplasmlc reticulum, thus preventing activation by proteolytic cleavage.