Structure of a human lysosomal sulfatase

Area of Science:

• Enzymology
• Structural Biology
• Biochemistry

Background:

• Sulfatases are enzymes that hydrolyze sulfuric acid esters from various substrates.
• Deficiencies in lysosomal sulfatases cause mucopolysaccharidoses, and multiple sulfatase deficiency results from a lack of post-translational modification of the active-site cysteine.
• Previous studies have identified the sulfatase active site and contributed to understanding these disorders.

Purpose of the Study:

• To determine the crystal structure of N-acetylgalactosamine-4-sulfatase.
• To elucidate the catalytic mechanism and substrate specificity of sulfatases.
• To understand the structural basis of sulfatase activity and related disorders.

Main Methods:

• X-ray crystallography was used to solve and refine the enzyme structure at 2.5 Å resolution.
• Structures were determined at cryogenic (123K) and room (273K) temperatures.
• Inhibitor complexes (vanadate) and product complexes (N-acetylgalactosamine) were also analyzed.

Main Results:

• The N-acetylgalactosamine-4-sulfatase structure reveals a two-domain fold with the active site in the larger domain.
• The active site contains a calcium ion, previously undetected, bound to the sulfate derivative of oxo-alanine at the Cys91 residue.
• A vanadate-inhibited structure shows vanadate covalently linked to the protein, replacing sulfate.

Conclusions:

• The structure suggests a conserved fold for the sulfatase family, with key residues stabilizing the calcium ion and sulfate ester.
• A catalytic role is proposed for the post-translationally modified cysteine residue.
• The active-site domain shows structural similarity to alkaline phosphatase, with conserved ion and substrate binding sites.