Arylsulfatase G inactivation causes loss of heparan sulfate 3-O-sulfatase activity and mucopolysaccharidosis in mice.

Deficiency of glycosaminoglycan (GAG) degradation causes a subclass of lysosomal storage disorders called mucopolysaccharidoses (MPSs), many of which present with severe neuropathology. Critical steps in the degradation of the GAG heparan sulfate remain enigmatic. Here we show that the lysosomal arylsulfatase G (ARSG) is the long-sought glucosamine-3-O-sulfatase required to complete the degradation of heparan sulfate. Arsg-deficient mice accumulate heparan sulfate in visceral organs and the central nervous system and develop neuronal cell death and behavioral deficits. This accumulated heparan sulfate exhibits unique nonreducing end structures with terminal N-sulfoglucosamine-3-O-sulfate residues, allowing diagnosis of the disorder. Recombinant human ARSG is able to cleave 3-O-sulfate groups from these residues as well as from an authentic 3-O-sulfated N-sulfoglucosamine standard. Our results demonstrate the key role of ARSG in heparan sulfate degradation and strongly suggest that ARSG deficiency represents a unique, as yet unknown form of MPS, which we term MPS IIIE.

Multiple gains of spliceosomal introns in a superfamily of vertebrate protease inhibitor genes.

BACKGROUND: Intron gains reportedly are very rare during evolution of vertebrates, and the mechanisms underlying their creation are largely unknown. Previous investigations have shown that, during metazoan radiation, the exon-intron patterns of serpin superfamily genes were subject to massive changes, in contrast to many other genes. RESULTS: Here we investigated intron dynamics in the serpin superfamily in lineages pre- and postdating the split of vertebrates. Multiple intron gains were detected in a group of ray-finned fishes, once the canonical groups of vertebrate serpins had been established. In two genes, co-occurrence of non-standard introns was observed, implying that intron gains in vertebrates may even happen concomitantly or in a rapidly consecutive manner. DNA breakage/repair processes associated with genome compaction are introduced as a novel factor potentially favoring intron gain, since all non-canonical introns were found in a lineage of ray-finned fishes that experienced genomic downsizing. CONCLUSION: Multiple intron acquisitions were identified in serpin genes of a lineage of ray-finned fishes, but not in any other vertebrates, suggesting that insertion rates for introns may be episodically increased. The co-occurrence of non-standard introns within the same gene discloses the possibility that introns may be gained simultaneously. The sequences flanking the intron insertion points correspond to the proto-splice site consensus sequence MAG upward arrowN, previously proposed to serve as intron insertion site. The association of intron gains in the serpin superfamily with a group of fishes that underwent genome compaction may indicate that DNA breakage/repair processes might foster intron birth.

Characterization of the human sulfatase Sulf1 and its high affinity heparin/heparan sulfate interaction domain.

The extracellular sulfatases Sulf1 and Sulf2 remodel the 6O-sulfation state of heparan sulfate proteoglycans on the cell surface, thereby modulating growth factor signaling. Different from all other sulfatases, the Sulfs contain a unique, positively charged hydrophilic domain (HD) of about 320 amino acid residues. Using various HD deletion mutants and glutathione S-transferase (GST)-HD fusion proteins, this study demonstrates that the HD is required for enzymatic activity and acts as a high affinity heparin/heparan sulfate interaction domain. Association of the HD with the cell surface is sensitive to heparinase treatment, underlining specificity toward heparan sulfate chains. Correspondingly, isolated GST-HD binds strongly to both heparin and heparan sulfate in vitro and also to living cells. Surface plasmon resonance studies indicate nanomolar affinity of GST-HD toward immobilized heparin. The comparison of different mutants reveals that especially the outer regions of the HD mediate heparan sulfate binding, probably involving "tandem" interactions. Interestingly, binding to heparan sulfate depends on the presence of 6O-sulfate substrate groups, suggesting that substrate turnover facilitates release of the enzyme from its substrate. Deletion of the inner, less conserved region of the HD drastically increases Sulf1 secretion without affecting enzymatic activity or substrate specificity, thus providing a tool for the in vitro modulation of HS-dependent signaling as demonstrated here for the signal transduction of fibroblast growth factor 2. Taken together, the present study shows that specific regions of the HD influence different aspects of HS binding, cellular localization, and enzyme function.

Formylglycine aldehyde Tag--protein engineering through a novel post-translational modification.

Oxidation of a specific cysteine residue to C(alpha)-formylglycine is a novel post-translational modification that is directed by a short recognition motif commonly found in pro- and eukaryotic sulfatases. As recently shown by C. Bertozzi and co-workers, this system can be employed in protein engineering to equip proteins with genetically encoded aldehyde tags for site-specific labeling, conjugation and immobilization.

Molecular basis of multiple sulfatase deficiency, mucolipidosis II/III and Niemann-Pick C1 disease - Lysosomal storage disorders caused by defects of non-lysosomal proteins.

Multiple sulfatase deficiency (MSD), mucolipidosis (ML) II/III and Niemann-Pick type C1 (NPC1) disease are rare but fatal lysosomal storage disorders caused by the genetic defect of non-lysosomal proteins. The NPC1 protein mainly localizes to late endosomes and is essential for cholesterol redistribution from endocytosed LDL to cellular membranes. NPC1 deficiency leads to lysosomal accumulation of a broad range of lipids. The precise functional mechanism of this membrane protein, however, remains puzzling. ML II, also termed I cell disease, and the less severe ML III result from deficiencies of the Golgi enzyme N-acetylglucosamine 1-phosphotransferase leading to a global defect of lysosome biogenesis. In patient cells, newly synthesized lysosomal proteins are not equipped with the critical lysosomal trafficking marker mannose 6-phosphate, thus escaping from lysosomal sorting at the trans Golgi network. MSD affects the entire sulfatase family, at least seven members of which are lysosomal enzymes that are specifically involved in the degradation of sulfated glycosaminoglycans, sulfolipids or other sulfated molecules. The combined deficiencies of all sulfatases result from a defective post-translational modification by the ER-localized formylglycine-generating enzyme (FGE), which oxidizes a specific cysteine residue to formylglycine, the catalytic residue enabling a unique mechanism of sulfate ester hydrolysis. This review gives an update on the molecular bases of these enigmatic diseases, which have been challenging researchers since many decades and so far led to a number of surprising findings that give deeper insight into both the cell biology and the pathobiochemistry underlying these complex disorders. In case of MSD, considerable progress has been made in recent years towards an understanding of disease-causing FGE mutations. First approaches to link molecular parameters with clinical manifestation have been described and even therapeutical options have been addressed. Further, the discovery of FGE as an essential sulfatase activating enzyme has considerable impact on enzyme replacement or gene therapy of lysosomal storage disorders caused by single sulfatase deficiencies.

Sulf loss influences N-, 2-O-, and 6-O-sulfation of multiple heparan sulfate proteoglycans and modulates fibroblast growth factor signaling.

Sulf1 and Sulf2 are two heparan sulfate 6-O-endosulfatases that regulate the activity of multiple growth factors, such as fibroblast growth factor and Wnt, and are essential for mammalian development and survival. In this study, the mammalian Sulfs were functionally characterized using overexpressing cell lines, in vitro enzyme assays, and in vivo Sulf knock-out cell models. Analysis of subcellular Sulf localization revealed significant differences in enzyme secretion and detergent solubility between the human isoforms and their previously characterized quail orthologs. Further, the activity of the Sulfs toward their native heparan sulfate substrates was determined in vitro, demonstrating restricted specificity for S-domain-associated 6S disaccharides and an inability to modify transition zone-associated UA-GlcNAc(6S). Analysis of heparan sulfate composition from different cell surface, shed, glycosylphosphatidylinositol-anchored and extracellular matrix proteoglycan fractions of Sulf knock-out cell lines established differential effects of Sulf1 and/or Sulf2 loss on nonsubstrate N-, 2-O-, and 6-O-sulfate groups. These findings indicate a dynamic influence of Sulf deficiency on the HS biosynthetic machinery. Real time PCR analysis substantiated differential expression of the Hs2st and Hs6st heparan sulfate sulfotransferase enzymes in the Sulf knock-out cell lines. Functionally, the changes in heparan sulfate sulfation resulting from Sulf loss were shown to elicit significant effects on fibroblast growth factor signaling. Taken together, this study implicates that the Sulfs are involved in a potential cellular feed-back mechanism, in which they edit the sulfation of multiple heparan sulfate proteoglycans, thereby regulating cellular signaling and modulating the expression of heparan sulfate biosynthetic enzymes.

Arylsulfatase G, a novel lysosomal sulfatase.

The sulfatases constitute a conserved family of enzymes that specifically hydrolyze sulfate esters in a wide variety of substrates such as glycosaminoglycans, steroid sulfates, or sulfolipids. By modifying the sulfation state of their substrates, sulfatases play a key role in the control of physiological processes, including cellular degradation, cell signaling, and hormone regulation. The loss of sulfatase activity has been linked with various severe pathophysiological conditions such as lysosomal storage disorders, developmental abnormalities, or cancer. A novel member of this family, arylsulfatase G (ASG), was initially described as an enzyme lacking in vitro arylsulfatase activity and localizing to the endoplasmic reticulum. Contrary to these results, we demonstrate here that ASG does indeed have arylsulfatase activity toward different pseudosubstrates like p-nitrocatechol sulfate and 4-methylumbelliferyl sulfate. The activity of ASG depends on the Cys-84 residue that is predicted to be post-translationally converted to the critical active site C(alpha)-formylglycine. Phosphate acts as a strong, competitive ASG inhibitor. ASG is active as an unprocessed 63-kDa monomer and shows an acidic pH optimum as typically seen for lysosomal sulfatases. In transfected cells, ASG accumulates within lysosomes as indicated by indirect immunofluorescence microscopy. Furthermore, ASG is a glycoprotein that binds specifically to mannose 6-phosphate receptors, corroborating its lysosomal localization. ARSG mRNA expression was found to be tissue-specific with highest expression in liver, kidney, and pancreas, suggesting a metabolic role of ASG that might be associated with a so far non-classified lysosomal storage disorder.

Homogeneous stalled ribosome nascent chain complexes produced in vivo or in vitro.

Cotranslational protein maturation is often studied in cell-free translation mixtures, using stalled ribosome-nascent chain complexes produced by translating truncated mRNA. This approach has two limitations: (i) it can be technically challenging, and (ii) it only works in vitro, where the concentrations of cellular components differ from concentrations in vivo. We have developed a method to produce stalled ribosomes bearing nascent chains of a specified length by using a 'stall sequence', derived from the Escherichia coli SecM protein, which interacts with residues in the ribosomal exit tunnel to stall SecM translation. When the stall sequence is expressed at the end of nascent chains, stable translation-arrested ribosome complexes accumulate in intact cells or cell-free extracts. SecM-directed stalling is efficient, with negligible effects on viability. This method is straightforward and suitable for producing stalled ribosome complexes in vivo, permitting study of the length-dependent maturation of nascent chains in the cellular milieu.