Structure of the elastase-cathepsin G inhibitor of the leech Hirudo medicinalis.

The leech Hirudo medicinalis contains three different groups of proteinase inhibitor proteins, the thrombin-specific hirudin, the bdellins directed against trypsin, plasmin and acrosin, and the eglins which were discovered only recently. We are interested in the eglins mainly for two reasons: (i) They form strong complexes with the granulocytic elastase and cathepsin G with Ki values close to 1 x 10(-10) mol/l. Due to this property they are potential candidates for the therapeutic treatment of various diseases. (ii) Although the eglins do not contain a disulfide bridge to stabilize the tertiary structure, they are highly resistant to denaturation by acidification and by heat as well as to proteolytic degradation.