Crystal structure of the parasite inhibitor chagasin in complex with papain allows identification of structural requirements for broad reactivity and specificity determinants for target proteases

• Published in: The FEBS journal Vol. 276; no. 3; pp. 793 - 806
• Main Authors: Redzynia, Izabela, Ljunggren, Anna, Bujacz, Anna, Abrahamson, Magnus, Jaskolski, Mariusz, Bujacz, Grzegorz
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.02.2009; Blackwell Publishing Ltd
• Subjects: Amino Acid Sequence; Animals; Biochemistry; Biochemistry and Molecular Biology; Biokemi och molekylärbiologi; Biologi; Biological Sciences; Chagas disease; Comparative studies; cruzipain; Crystal structure; Crystallography, X-Ray; Cysteine Endopeptidases - chemistry; Cysteine Endopeptidases - metabolism; cysteine proteases; Cysteine Proteinase Inhibitors - chemistry; Cysteine Proteinase Inhibitors - genetics; Cysteine Proteinase Inhibitors - metabolism; Cysteine Proteinase Inhibitors - pharmacology; cysteine proteinases; Enzyme Activation - drug effects; Inhibitor drugs; inhibitors; Kinetics; Models, Molecular; Natural Sciences; Naturvetenskap; papain; Papain - chemistry; Papain - metabolism; Parasites; protein; Protein Binding; protein inhibitors; Protein Structure, Quaternary; Protozoan Proteins - chemistry; Protozoan Proteins - genetics; Protozoan Proteins - metabolism; Protozoan Proteins - pharmacology; Sequence Alignment; Substrate Specificity; Trypanosoma cruzi - chemistry; Trypanosoma cruzi - genetics; Trypanosoma cruzi - metabolism
• ISSN: 1742-464X; 1742-4658
• DOI: 10.1111/j.1742-4658.2008.06824.x

A complex of chagasin, a protein inhibitor from Trypanosoma cruzi, and papain, a classic family C1 cysteine protease, has been crystallized. Kinetic studies revealed that inactivation of papain by chagasin is very fast (kon = 1.5 x 10⁶ m⁻¹·s⁻¹), and results in the formation of a very tight, reversible complex (Ki = 36 p m), with similar or better rate and equilibrium constants than those for cathepsins L and B. The high-resolution crystal structure shows an inhibitory wedge comprising three loops, which forms a number of contacts responsible for the high-affinity binding. Comparison with the structure of papain in complex with human cystatin B reveals that, despite entirely different folding, the two inhibitors utilize very similar atomic interactions, leading to essentially identical affinities for the enzyme. Comparisons of the chagasin-papain complex with high-resolution structures of chagasin in complexes with cathepsin L, cathepsin B and falcipain allowed the creation of a consensus map of the structural features that are important for efficient inhibition of papain-like enzymes. The comparisons also revealed a number of unique interactions that can be used to design enzyme-specific inhibitors. As papain exhibits high structural similarity to the catalytic domain of the T. cruzi enzyme cruzipain, the present chagasin-papain complex provides a reliable model of chagasin-cruzipain interactions. Such information, coupled with our identification of specificity-conferring interactions, should be important for the development of drugs for treatment of the devastating Chagas disease caused by this parasite.