Crystal structure of protein C inhibitor provides insights into hormone binding and heparin activation |
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Authors: | Huntington James A Kjellberg Margareta Stenflo Johan |
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Affiliation: | Department of Haematology, Division of Structural Medicine, University of Cambridge, Cambridge Institute for Medical Research, Wellcome Trust/MRC Building, Hills Road, CB2 2XY, Cambridge, United Kingdom. jah52@cam.ac.uk |
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Abstract: |  Protein C inhibitor (PCI) is a member of the serpin family that has many biological functions. In blood it acts as a procoagulant, and, in the seminal vesicles, it is required for spermatogenesis. The activity of PCI is affected by heparin binding in a manner unique among the heparin binding serpins, and, in addition, PCI binds hydrophobic hormones with apparent specificity for retinoids. Here we present the 2.4 A crystallographic structure of reactive center loop (RCL) cleaved PCI. A striking feature of the structure is a two-turn N-terminal shortening of helix A, which creates a large hydrophobic pocket that docking studies indicate to be the retinoid binding site. On the basis of surface electrostatic properties, a novel mechanism for heparin activation is proposed. |
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