Heparan N-sulfatase: cysteine 70 plays a role in the enzyme catalysis and processing

Sulfatases are members of a highly conserved family of enzymes that catalyze the hydrolysis of sulfate ester bonds from a variety of substrates. The functional correlation reflects a high degree of amino acid sequence similarity along the entire length, in particular in the active site where the C(X)PSR consensus sequence is present. Cysteine undergoes an important co- or post-translation modification essential for the accomplishment of catalytic activity: conversion in formylglycine. In this work, the cysteine of heparan N-sulfatase (NS) was replaced either by a serine (C70S) or by a methionine (C70M) using site-directed mutagenesis. C70S and C70M mutant cDNAs were expressed and analyzed in COS cells; both mutations caused a loss of NS activity; however, while C70S showed a normal precursor form undergoing processing to a reduced mature form within the lysosomes, C70M was poorly synthesized and formed a complex with the molecular chaperone immunoglobulin binding protein.