Structural characterization of thyroglobulin type-1 domains of equistatin.
Equistatin is a protein composed of three thyroglobulin type-1 domains. It inhibits papain-like cysteine proteinases and the aspartic proteinase, cathepsin D. To determine the structural basis for this inhibition we cloned and expressed the separated domains (eq d-1, eq d-2, eq d-3) in Pichia pastoris. Kinetic constants for the interaction of eq d-1 with papain and that of eq d-2 with cathepsin D are of similar order (subnanomolar) and are comparable to the constants obtained for full-length equistatin. The target proteinase for the third domain remains unknown. Thus, we demonstrate here that thyroglobulin type-1 motifs per se are able to support specific structural features that enable them to inhibit proteases from different classes. The overall conformation of three domains in equistatin is such that the interaction of domains 1 or 2 with their respective target enzymes is not hindered sterically by either domain. In addition, we show that the interaction of eq d-2 with cathepsin D results in conformational changes, which is not the case for the eq d-1/papain interaction.
Galesa
Katja
K
Department of Biochemistry and Molecular Biology, J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
Pain
Roger
R
Jongsma
Maarten A
MA
Turk
Vito
V
Lenarcic
Brigita
B
D002402:Cathepsin D / Q000037:antagonists & inhibitors; D002942:Circular Dichroism; D003001:Cloning, Molecular; D007700:Kinetics; D010206:Papain / Q000378:metabolism; D010843:Pichia; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D013954:Thyroglobulin / Q000737:chemistry
D011506:Proteins; D011994:Recombinant Proteins; C106356:equistatin; D013954:Thyroglobulin; D010206:Papain; D002402:Cathepsin D