Inhibitory peptide of papain-like cysteine proteases, affinity selected from a random disulfide constrained phage-displayed peptide library, was grafted to staphylococcal protein A's B domain. Scaffold protein was additionally modified in order to allow solvent exposed display of peptide loop. Correct folding of fusion proteins was confirmed by CD-spectroscopy and by the ability to bind the Fc-region of rabbit IgG, a characteristic of parent domain. The recombinant constructs inhibited cathepsin L with inhibitory constants in the low-micromolar range. (c) 2006 Elsevier Inc. All rights reserved.