PMID: 16601115 , Related PDB id: 2CH9

Authors:

Schuttelkopf AW, Hamilton G, Watts C, van Aalten DM

Title:

Structural basis of reduction-dependent activation of human cystatin F.

Journal:

J Biol Chem. 2006 Jun 16;281(24):16570-5. Epub 2006 Apr 6.

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.