title: A 2.6 A structure of a serpin polymer and implications for conformational disease.
abstract: The function of the serpins as proteinase inhibitors depends on their ability to insert the cleaved reactive centre loop as the fourth strand in the main A beta-sheet of the molecule upon proteolytic attack at the reactive centre, P1-P1'. This mechanism is vulnerable to mutations which result in inappropriate intra- or intermolecular loop insertion in the absence of cleavage. Intermolecular loop insertion is known as serpin polymerisation and results in a variety of diseases, most notably liver cirrhosis resulting from mutations of the prototypical serpin alpha1-antitrypsin. We present here the 2.6 A structure of a polymer of alpha1-antitrypsin cleaved six residues N-terminal to the reactive centre, P7-P6 (Phe352-Leu353). After self insertion of P14 to P7, intermolecular linkage is affected by insertion of the P6-P3 residues of one molecule into the partially occupied beta-sheet A of another. This results in an infinite, linear polymer which propagates in the crystal along a 2-fold screw axis. These findings provide a framework for understanding the uncleaved alpha1-antitrypsin polymer and fibrillar and amyloid deposition of proteins seen in other conformational diseases, with the ordered array of polymers in the crystal resulting from slow accretion of the cleaved serpin over the period of a year.
authors.affiliation: Division of Structural Medicine, Department of Haematology, University of Cambridge, Cambridge Institute for Medical Research, Cambridge, CB2 2XY, UK.
authors.forename: J A
authors.initials: JA
authors.lastname: Huntington
authors.forename: N S
authors.initials: NS
authors.lastname: Pannu
authors.forename: B
authors.initials: B
authors.lastname: Hazes
authors.forename: R J
authors.initials: RJ
authors.lastname: Read
authors.forename: D A
authors.initials: DA
authors.lastname: Lomas
authors.forename: R W
authors.initials: RW
authors.lastname: Carrell
mesh_terms: D000595:Amino Acid Sequence; D003460:Crystallization; D018360:Crystallography, X-Ray; D006801:Humans; D008103:Liver Cirrhosis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D058225:Plaque, Amyloid / Q000378:metabolism / Q000473:pathology; D011108:Polymers; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013997:Time Factors; D000515:alpha 1-Antitrypsin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D010446:Peptide Fragments; D011108:Polymers; D011994:Recombinant Proteins; D000515:alpha 1-Antitrypsin