Three-dimensional structure of human lysosomal aspartylglucosaminidase

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Abstract
The high resolution crystal structure of human lysosomal aspartylglucosaminidase (AGA) has been determined. This lysosomal enzyme is synthesized as a single polypeptide precursor, which is immediately post-translationally cleaved into α- and β-subunits. Two α- and β-chains are found to pack together forming the final heterotetrameric structure. The catalytically essential residue, the N-terminal threonine of the β-chain is situated in the deep pocket of the funnel-shaped active site. On the basis of the structure of the enzyme–product complex we present a catalytic mechanism for this lysosomal enzyme with an exceptionally high pH optimum. The three-dimensional structure also allows the prediction of the structural consequences of human mutations resulting in aspartylglucosaminuria (AGU), a lysosomal storage disease.