POSTTRANSLATIONAL FORMATION OF FORMYLGLYCINE IN PROKARYOTIC SULFATASES BY MODIFICATION OF EITHER CYSTEINE OR SERINE

Eukaryotic sulfatases carry an alpha-formylglycine residue that is ess ential for activity and is located within the catalytic site. This for mylglycine is generated by posttranslational modification of a conserv ed cysteine residue. The arylsulfatase gene of Pseudomonas aeruginosa also encodes a cysteine at the critical position. This protein could b e expressed in active form in a sulfatase-deficient strain of P. aerug inosa, thereby restoring growth on aromatic sulfates as sole sulfur so urce, and in Escherichia coli, Analysis of the mature protein expresse d in E. coli revealed the presence of formylglycine at the expected po sition, showing that the cysteine is also converted to formylglycine i n a prokaryotic sulfatase. Substituting the relevant cysteine by a ser ine codon in the P. aeruginosa gene led to expression of inactive sulf atase protein, lacking the formylglycine. The machinery catalyzing the modification of the Pseudomonas sulfatase in E. coli therefore resemb les the eukaryotic machinery, accepting cysteine but not serine as a m odification substrate, By contrast, in the arylsulfatase of Klebsiella pneumoniae a formylglycine is found generated by modification of a se rine residue. The expression of both the Klebsiella and the Pseudomona s sulfatases as active enzymes in E. coli suggests that two modificati on systems are present, or that a common modification system is modula ted by a cofactor.