title: 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.
abstract: 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 (k(on) = 1.5 x 10(6) M(-1) x s(-1)), and results in the formation of a very tight, reversible complex (K(i) = 36 pM), 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.
authors.affiliation: Institute of Technical Biochemistry, Faculty of Biotechnology and Food Sciences, Technical University of Lodz, Poland.
authors.forename: Izabela
authors.initials: I
authors.lastname: Redzynia
authors.forename: Anna
authors.initials: A
authors.lastname: Ljunggren
authors.forename: Anna
authors.initials: A
authors.lastname: Bujacz
authors.forename: Magnus
authors.initials: M
authors.lastname: Abrahamson
authors.forename: Mariusz
authors.initials: M
authors.lastname: Jaskolski
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Bujacz
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018360:Crystallography, X-Ray; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D008958:Models, Molecular; D010206:Papain / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D015800:Protozoan Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D016415:Sequence Alignment; D013379:Substrate Specificity; D014349:Trypanosoma cruzi / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D015853:Cysteine Proteinase Inhibitors; D015800:Protozoan Proteins; C435145:chagasin, Trypanosoma; D003546:Cysteine Endopeptidases; D010206:Papain; C063214:cruzipain