Thrombin Activatable Fibrinolysis inhibitor (TAFI) is a basic carboxypeptidase, circulating in plasma as an enzymatic inactive precursor. TAFI shares ~40% overall sequence identity with pancreas Carboxypeptidase B (PCPB) with the activation peptide being less conserved. Following activation of TAFI we observed a change in the isoelectric point (IP) of TAFIa. The IP of TAFIa was significantly more basic than the IP of TAFI. This was not observed in PCPB. Due to the change in IP, we have investigated the structural basis for this observation by mapping the N- and O-linked glycans. TAFI has 5 potential N-linked glycosylation sites, four of them located on the activation peptide. Only one potential O-linked glycosylation site is seen. In addition, TAFIa is unstable and loose enzymatic activity quickly. This is in contrast to the homologous PCPB. The structural basis for this observation is not known but could be caused by differences in thermodynamic stability. Disulfides are a major contributor to the structural integrity of proteins and disulfide permutations could explain the difference in enzymatic stability. To test this hypothesis we have identified the disulfide pattern of the eight cysteines in TAFI. In this study we have purified and characterized TAFI from human plasma.
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1st Latin American Protein Society meeting brazil, 2004