title: The structure of human GALNS reveals the molecular basis for mucopolysaccharidosis IV A.
abstract: Lysosomal enzymes catalyze the breakdown of macromolecules in the cell. In humans, loss of activity of a lysosomal enzyme leads to an inherited metabolic defect known as a lysosomal storage disorder. The human lysosomal enzyme galactosamine-6-sulfatase (GALNS, also known as N-acetylgalactosamine-6-sulfatase and GalN6S; E.C. 3.1.6.4) is deficient in patients with the lysosomal storage disease mucopolysaccharidosis IV A (also known as MPS IV A and Morquio A). Here, we report the three-dimensional structure of human GALNS, determined by X-ray crystallography at 2.2Å resolution. The structure reveals a catalytic gem diol nucleophile derived from modification of a cysteine side chain. The active site of GALNS is a large, positively charged trench suitable for binding polyanionic substrates such as keratan sulfate and chondroitin-6-sulfate. Enzymatic assays on the insect-cell-expressed human GALNS indicate activity against synthetic substrates and inhibition by both substrate and product. Mapping 120 MPS IV A missense mutations onto the structure reveals that a majority of mutations affect the hydrophobic core of the structure, indicating that most MPS IV A cases result from misfolding of GALNS. Comparison of the structure of GALNS to paralogous sulfatases shows a wide variety of active-site geometries in the family but strict conservation of the catalytic machinery. Overall, the structure and the known mutations establish the molecular basis for MPS IV A and for the larger MPS family of diseases.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Massachusetts Amherst, Amherst, MA 01003, USA.
authors.forename: Yadilette
authors.initials: Y
authors.lastname: Rivera-Colón
authors.forename: Emily K
authors.initials: EK
authors.lastname: Schutsky
authors.forename: Adriana Z
authors.initials: AZ
authors.lastname: Kita
authors.forename: Scott C
authors.initials: SC
authors.lastname: Garman
mesh_terms: D000818:Animals; D020134:Catalytic Domain; D002460:Cell Line; D002811:Chondroitinsulfatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D006801:Humans; D007313:Insecta; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D009085:Mucopolysaccharidosis IV / Q000235:genetics*; D020125:Mutation, Missense; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D008024:Ligands; D002811:Chondroitinsulfatases; C102295:GALNS protein, human