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Biological Chemistry

Editor-in-Chief: Brüne, Bernhard

Editorial Board Member: Buchner, Johannes / Ludwig, Stephan / Sies, Helmut / Turk, Boris / Wittinghofer, Alfred

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Analysis of an engineered plasma kallikrein inhibitor and its effect on contact activation

A. Allart Stoop1, a / Ravi V. Joshi1 / Christopher T. Eggers1, b / Charles S. Craik1

1Department of Pharmaceutical Chemistry, University of California San Francisco, 600 16th Street Suite # S512, San Francisco, CA 94143-2280, USA

aPresent address: Domantis Ltd., 315 Cambridge Science Park, Cambridge CB4 0WG, UK.

bPresent address: Department of Chemistry, University of California, San Diego, CA 92093, USA.

Corresponding author

Citation Information: Biological Chemistry. Volume 391, Issue 4, Pages 425–433, ISSN (Online) 1437-4315, ISSN (Print) 1431-6730, DOI: 10.1515/bc.2010.047, February 2010

Publication History

Published Online:


Engineering of protein-protein interactions is used to enhance the affinity or specificity of proteins, such as antibodies or protease inhibitors, for their targets. However, fully diversifying all residues in a protein-protein interface is often unfeasible. Therefore, we limited our phage library for the serine protease inhibitor ecotin by restricting it to only tetranomial diversity and then targeted all 20 amino acid residues involved in protein recognition. This resulted in a high-affinity and highly specific plasma kallikrein inhibitor, ecotin-Pkal. To validate this approach we dissected the energetic contributions of each wild type (wt) or mutated surface loop to the binding of either plasma kallikrein (PKal) or membrane-type serine protease 1. The analysis demonstrated that a mutation in one loop has opposing effects depending on the sequence of surrounding loops. This finding stresses the cooperative nature of loop-loop interactions and justifies targeting multiple loops with a limited diversity. In contrast to ecotin wt, the specific loop combination of ecotin-Pkal discriminates the subtle structural differences between the active enzymes, PKal and Factor XIIa, and their respective zymogen forms. We used ecotin-Pkal to specifically inhibit contact activation of human plasma at the level mediated by plasma kallikrein.

Keywords: cooperativity; plasma kallikrein; protease inhibitors; protein engineering; specificity

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