Functional Principles of Legumain Inhibition by Macrocypin



The lysosomal cysteine protease legumain is a key example of how manifold the ways are nature implemented to regulate protease activity. In the first place it is synthesized as an inactive proenzyme. Activation to its endo- and exo-protease activities occurs via pH-shift and/or proteolytic processing within the endo-lysosomal system. Here, legumain is a key player of our immune system via its function in processing of antigens for presentation on the MHCII complex. The active enzyme specifically cleaves after asparagine residues and is stable at acidic pH, but once activated becomes unstable at neutral pH. However, pH-stabilization is possible for example by binding to its prodomain or integrin avb3. On top of that, legumain harbours a pH-dependent peptide ligase activity, i.e. legumain can not only hydrolyze peptide bonds, but it can also synthesize them. Overexpression and dislocation of legumain from the endo-lysosomal system is associated with severe pathologies like cancer and Alzheimer’s disease. However, how exactly its enzymatic activity or which of its activities are involved is still not understood in every detail. Therefore specific inhibitors of its enzymatic activities are much sought after. Different inhibitors could be identified, including its prodomain, synthetic peptide inhibitors and naturally occurring protein inhibitors of the cystatin and macrocypin family. While there is already a significant body of knowledge on the interaction of legumain with cystatins, only little is known on its regulation by macrocypins. Macrocypins are a family of fungal protease inhibitors that harbour a versatile surface which allows them to inhibit different classes of proteases at the same time. The macrocypin fold is further characterized by high resistance towards extremes of pH and temperature, which together makes them attractive starting points for biotechnological and medical applications.

Within this proposal we aim to elucidate the mode of interaction of macrocypins with legumain by combining biochemical, biophysical and structural techniques. The project will be conducted at the University of Salzburg, at the Structural Biology group headed by Prof. Dr. Johann Brandstetter under the supervision of Dr. Elfriede Dall. The newly acquired knowledge will serve as a basis for the design of versatile, selective legumain inhibitors which can be further exploited as a new scaffold for drug development
Tatsächlicher Beginn/ -es Ende1/07/1930/06/22