title: Antithrombin III Budapest: a single amino acid substitution (429Pro to Leu) in a region highly conserved in the serpin family.
abstract: Antithrombin III (AT) is a major plasma serine protease inhibitor and a member of the serpin family of proteins. We have characterized the molecular and genetic basis of AT Budapest, an inherited variant of AT that is associated with thrombotic disease in affected family members. A single amino acid substitution, 429Pro to Leu, was identified, occurring in a region of the molecule that is highly conserved in members of the serpin family. Two forms of variant protein were present in approximately equal amounts in the plasma of the propositus, who is homozygous for the mutation. One form, which had apparently normal Mr, bound heparin strongly and retained some residual thrombin inhibitory activity. The other form had only weak heparin affinity and no antiproteinase activity, and had slightly decreased mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under nonreducing conditions; this normalized in the presence of a reducing agent, suggesting it was caused by a change in conformation. Additional support for a difference in conformation of the two forms of variant was provided by the finding that the fraction that bound heparin-Sepharose was recognized by a monoclonal antibody raised against normal AT, whereas the weak-affinity fraction was not.
authors.affiliation: Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, England.
authors.forename: R J
authors.initials: RJ
authors.lastname: Olds
authors.forename: D A
authors.initials: DA
authors.lastname: Lane
authors.forename: R
authors.initials: R
authors.lastname: Caso
authors.forename: M
authors.initials: M
authors.lastname: Panico
authors.forename: H R
authors.initials: HR
authors.lastname: Morris
authors.forename: G
authors.initials: G
authors.lastname: Sas
authors.forename: J
authors.initials: J
authors.lastname: Dawes
authors.forename: S L
authors.initials: SL
authors.lastname: Thein
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal; D000990:Antithrombin III / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D004247:DNA / Q000737:chemistry; D006493:Heparin / Q000378:metabolism; D006720:Homozygote; D006801:Humans; D007930:Leucine; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D011392:Proline; D013917:Thrombin / Q000037:antagonists & inhibitors; D013923:Thromboembolism / Q000097:blood* / Q000235:genetics
chemical_list: D000911:Antibodies, Monoclonal; C055367:antithrombin III Budapest 2; D000990:Antithrombin III; D006493:Heparin; D004247:DNA; D011392:Proline; D013917:Thrombin; D007930:Leucine