Heparan sulfate (HS) are complex polysaccharides abundantly found in extracellular matrices and cell surfaces. These polysaccharides participate to major cellular processes through their ability to bind and modulate a wide array of signalling proteins. HS/ligands interactions occur through saccharide domains (termed S-domains) of specific sulfation pattern, present within the polysaccharide. Assembly of such functional domains is orchestrated by a complex biosynthesis machinery and their structure is further regulated at the cell surface by post-synthetic modifying enzymes, including extracellular sulfatases of the Sulf family. Sulfs specifically target HS S-domains and catalyze the selective removal of 6-O-sulfate groups, which are required for the recognition of many proteins. Although structurally subtle, these modifications have great functional consequences, and Sulfs have emerged as critical regulators of HS activity, in physiological processes such as embryogenesis and tissue regeneration, and in diseases such as cancer. There are two identified isoforms of Sulfs, Sulf-1 and Sulf-2, which share a very similar molecular organization. They are composed of two regions that are essential for enzyme activity: the catalytic domain (CAT-D), which includes the enzyme active site and is well conserved amongst sulfatases, and a highly basic, hydrophilic domain (Hyd-D), which is responsible for recognition and binding to HS substrates and is a unique feature of the Sulfs. However, despite increasing interest, Sulfs still remain poorly understood. During our recent studies of these enzymes, we have shed light on an original processive desulfation mechanism and on remarkable structural features. Based on these data, the SULF@AS project proposes to deliver an integrated study of the human isoforms HSulf-1 and HSulf-2, combining biochemical and biophysical approaches to characterize their structure and post-translational modifications ; in vitro, in cellulo and in vivo functional analysis to determine their substrate specificities and respective role during tumour progression ; and the development of specific inhibitors based on HS mimetics. This project should provide major insights into the regulatory role played by these enzymes in many biological processes and deliver the structural basis for the development of therapeutic strategies targeting HSulfs.