Role of Arylsulfatase K (ARSK) in lysosomal function in health and disease

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In human, sulfatases constitute a family of 17 enzymes that are responsible for the hydrolysis of sulfate esters in a variety of substrates like glycosaminoglycans (GAGs). As each sulfatase shows a strict specificity towards its physiological substrate, the lysosomal degradation of GAGs like heparan sulfate, carrying complex sulfation patterns, needs the activity of several sulfatases - including as yet uncharacterized sulfatases. As a consequence, deficiency of any enzyme involved in the sequential degradation pathway of GAGs results in a subclass of lysosomal storage diseases called mucopolysaccharidoses which is characterized by the accumulation of GAGs as storage material. Recently, we have validated the lysosomal localization of the newly discovered arylsulfatase K (ARSK) and demonstrated desulfation activity of recombinant human ARSK towards arylsulfates serving as pseudosubstrates. In this proposal we aim to identify the physiological substrate of ARSK by studying a constitutive knock out mouse model for Arsk-deficiency. Therefore, we have already generated such a mouse model and we plan to characterize this model regarding the manifestation of a lysosomal storage disease. We will analyze the mouse model regarding behavioral, histological, cellular and biochemical alterations. As a focus of this project, we will isolate the lysosomal storage material and determine its nature and molecular structure in order to identify the physiological substrate of ARSK. As a final proof, we will desulfate the isolated substrate in vitro using recombinant ARSK derived from overexpressing CHO or insect cells.