alpha-N-acetylgalactosaminidase (alpha-NAGAL; E.C. 3.2.1.49) is a lysosomal 
exoglycosidase that cleaves terminal alpha-N-acetylgalactosamine residues from 
glycopeptides and glycolipids. In humans, a deficiency of alpha-NAGAL activity 
results in the lysosomal storage disorders Schindler disease and Kanzaki 
disease. To better understand the molecular defects in the diseases, we 
determined the crystal structure of human alpha-NAGAL after expressing wild-type 
and glycosylation-deficient glycoproteins in recombinant insect cell expression 
systems. We measured the enzymatic parameters of our purified wild-type and 
mutant enzymes, establishing their enzymatic equivalence. To investigate the 
binding specificity and catalytic mechanism of the human alpha-NAGAL enzyme, we 
determined three crystallographic complexes with different catalytic products 
bound in the active site of the enzyme. To better understand how individual 
defects in the alpha-NAGAL glycoprotein lead to Schindler disease, we analyzed 
the effect of disease-causing mutations on the three-dimensional structure.