Antithrombin III Budapest: a single amino acid substitution (429Pro to Leu)
in a region highly conserved in the serpin family
RJ Olds, DA Lane, R Caso, M Panico, HR Morris, G Sas, J Dawes and SL Thein
Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, England.
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.
Volume 79,
Issue 5,
pp. 1206-1212,
03/01/1992
Copyright © 1992 by The American Society of Hematology
