The reactive site loop of the serpin family of serine proteinase inhibitors is flexible and can adopt a number of diverse conformations. A 2.9 A resolution structure of alpha 1-antitrypsin-the principal proteinase inhibitor in human plasma-shows the loop in a stable canonical conformation matching that found in all other families of serine proteinase inhibitors ...
The reactive site loop of the serpin family of serine proteinase inhibitors is flexible and can adopt a number of diverse conformations. A 2.9 A resolution structure of alpha 1-antitrypsin-the principal proteinase inhibitor in human plasma-shows the loop in a stable canonical conformation matching that found in all other families of serine proteinase inhibitors. This unexpected finding in the absence of loop insertion into the body of the molecule favours a two-stage mechanism of inhibition and provides a model for the heparin activation of antithrombin. The beta-pleated strand conformation of the loop also accounts for the polymerization of the serpins in disease and for their association with other beta-sheet structures, most notably the beta-amyloid of Alzheimer's disease.
Organizational Affiliation:
Department of Haematology, University of Cambridge, UK.
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