Biochemical and Structural Insights into an Allelic Variant Causing the Lysosomal Storage Disorder Aspartylglucosaminuria.

Aspartylglucosaminuria (AGU) is a lysosomal storage disorder caused by defects of the hydrolase glycosylasparaginase (GA). Previously, we showed that a Canadian AGU mutation disrupts an obligatory intra-molecular autoprocessing with the enzyme trapped as an inactive precursor. Here, we report biochemical and structural characterizations of a model enzyme corresponding to a Finnish AGU allele, the T234I variant. Unlike the Canadian counterpart, the Finnish variant is capable of a slow autoprocessing to generate detectible hydrolyzation activity of the natural substrate of GA. We have determined a 1.6 A-resolution structure of the Finnish AGU model and built an enzyme-substrate complex to provide a structural basis for analyzing the negative effects of the point mutation on KM and kcat of the mature enzyme.