Arylsulfatase A (ASA) hydrolyzes sulfate esters with a pH optimum of 5. Interactions between p-nitrocatechol sulfate (NCS, artificial substrate) and active site residues of ASA are revealed from their co-crystal structure. Since equivalent ASA interactions with its natural substrates, sulfogalactosylceramide (SGC) and sulfogalactosylglycerolipid (SGG), are not known, we computationally docked SGC/SGG to the ASA crystal structure. Our dockings suggested that Cys69 was the active site residue, and Lys302 & Lys123 as residues anchoring the sulfate group of SGC/SGG to the active site, as observed for NCS. We further confirmed these results using 2 recombinant ASA mutants: C69A and CKK (Cys69, Lys302 and Lys123-all mutated to Ala). Both ASA mutants failed to desulfate SGC/SGG, and CKK showed minimal binding to [(14)C]SGC, although C69A still had affinity for this sulfoglycolipid. However, our dockings suggested additional intermolecular hydrogen bonding and hydrophobic interactions between ASA and SGC/SGG, thus contributing to the specificity of SGC/SGG as natural substrates.
Arylsulfatase A (AS-A) is a lysosomal enzyme, which catalyzes the desulfation of certain sulfogalactolipids, including sulfogalactosylglycerolipid (SGG), a molecule implicated in cell adhesion. In this report, immunocytochemistry revealed the selective presence of AS-A in the corpus luteum of mouse ovaries. Immunoblotting indicated that mouse corpus luteum AS-A had a molecular mass of 66 kDa, similar to AS-A of other tissues. Corpus luteum AS-A was active, capable of desulfating the artificial substrate, p-nitrocatechol sulfate, at the optimum pH of five. To understand further the role of AS-A in female reproduction, levels of AS-A were determined during corpus luteum development in pseudopregnant mice and during luteolysis after cessation of pseudopregnancy. Immunocytochemistry, immunoblotting and desulfation activity showed that AS-A expression was evident at the onset of pseudopregnancy in the newly formed corpora lutea, and its level increased steadily during gland development. The increase in the expression and activity of AS-A continued throughout luteolysis after the decrease in serum progesterone levels. We also observed the selective presence of SGG on the luteal cell surface in developed corpora lutea, as shown by immunofluorescence of mouse ovary sections as well as high-performance thin-layer chromatography of lipids isolated from mouse and pig corpora lutea. The identity of the "SGG" band on the thin layer silica plate was further validated by electrospray ionization mass spectrometry. Significantly, SGG disappeared in regressing corpora lutea. Therefore, lysosomal AS-A may be involved in cell-surface remodeling during luteolysis by desulfating SGG after its endocytosis and targeting to the lysosome.
Zusammenfassung: Das umlagenfinanzierte System der gesetzlichen Rentenversicherung als alleinige Lebensstandardsicherung stößt durch die demografische Entwicklung an seine Grenzen. Zur Aufrechterhaltung der Funktionsfähigkeit der gesetzlichen Rentenversicherung führt der Staat dem System Bundesmittel in Milliardenhöhe zu, Tendenz steigend. Um die Versorgungslücken der gesetzlichen Rentenversicherung zu schließen, kommt der privaten Altersvorsorge stetig wachsende Bedeutung zu. Hierzu hat der Gesetzgeber durch die Einführung der Rahmenbedingungen für eine staatlich geförderte „kapitalgedeckte private Altersvorsorge“ (sog. Riester-Rente) bereits in der Vergangenheit einen wichtigen Betrag geleistet. Leider hat der eingeschlagene Weg bislang noch nicht den nötigen Verbreitungsgrad erreicht, was auch daran liegt, dass das System noch nicht optimal einjustiert ist. Die Folgen einer unzureichenden Altersvorsorge zwingen zum politischen Handeln. Vor dem Hintergrund der analysierten Problemfelder soll mit dem Hessischen Konzept der Deutschland-Rente das bestehende System der privaten Altersvorsorge verbessert und gestärkt werden. Damit der Sparer langfristig von den Renditechancen des Kapitalmarktes profitieren kann, müssen u. a. die starren Garantievorgaben gelockert werden. Zugleich muss eine kostengünstige und transparente Alternative zu den bisherigen Riester-Produkten der privaten Anbieter geschaffen werden. Darum soll ein staatlich organisierter Fonds ein Anlageprodukt anbieten – den sog. Deutschlandfonds –, der auf Selbstkostenbasis operiert, aber ansonsten den allgemeinen Wettbewerbsbedingungen unterliegt. Damit soll ganz bewusst eine Konkurrenz zu den Produkten der etablierten Anbieter geschaffen werden. Im Ergebnis sollen die privaten Anbieter durch den Deutschlandfonds animiert werden, ihre Produkte attraktiver zu gestalten.
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