title: Structural basis of reduction-dependent activation of human cystatin F.
abstract: Cystatins are important natural cysteine protease inhibitors targeting primarily papain-like cysteine proteases, including cathepsins and parasitic proteases like cruzipain, but also mammalian asparaginyl endopeptidase. Mammalian cystatin F, which is expressed almost exclusively in hematopoietic cells and accumulates in lysosome-like organelles, has been implicated in the regulation of antigen presentation and other immune processes. It is an unusual cystatin superfamily member with a redox-regulated activation mechanism and a restricted specificity profile. We describe the 2.1A crystal structure of human cystatin F in its dimeric "off" state. The two monomers interact in a fashion not seen before for cystatins or cystatin-like proteins that is crucially dependent on an unusual intermolecular disulfide bridge, suggesting how reduction leads to monomer formation and activation. Strikingly, core sugars for one of the two N-linked glycosylation sites of cystatin F are well ordered, and their conformation and interactions with the protein indicate that this unique feature of cystatin F may modulate its inhibitory properties, in particular its reduced affinity toward asparaginyl endopeptidase compared with other cystatins.
authors.affiliation: Division of Biological Chemistry and Molecular Microbiology, Wellcome Trust Biocentre, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland.
authors.forename: Alexander W
authors.initials: AW
authors.lastname: Schüttelkopf
authors.forename: Garth
authors.initials: G
authors.lastname: Hamilton
authors.forename: Colin
authors.initials: C
authors.lastname: Watts
authors.forename: Daan M F
authors.initials: DM
authors.lastname: van Aalten
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D014408:Biomarkers, Tumor / Q000737:chemistry*; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D018360:Crystallography, X-Ray / Q000379:methods; D015891:Cystatins / Q000737:chemistry*; D003546:Cysteine Endopeptidases / Q000737:chemistry; D019281:Dimerization; D006031:Glycosylation; D006639:Histidine / Q000737:chemistry; D006801:Humans; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D000099240:Asparaginyl Endopeptidase
chemical_list: D014408:Biomarkers, Tumor; D015891:Cystatins; D003546:Cysteine Endopeptidases; D006639:Histidine; D000099240:Asparaginyl Endopeptidase; C116891:CST7 protein, human