Characterization of γ-carboxylated tryptic peptides by collision-induced dissociation and electron transfer dissociation mass spectrometry.

Vitamin K-dependent carboxylation of glutamic acid (Glu) residues into γ-carboxyglutamic acid (Gla) is a post-translational modification essential for normal protein activity of, for example, proteins involved in the blood coagulation system. These proteins may contain as many as 12 sites for γ-carboxylation within a protein sequence of 45 amino acid residues. In the biopharmaceutical industry, powerful analytical techniques are required for identification and localization of modified sites. We here present comparatively easy and rapid methods for studies of Gla-containing proteins using recent technology. The performances of two mass spectrometric fragmentation techniques, collision-induced dissociation (CID) and electron transfer dissociation (ETD), were evaluated with respect to γ-carboxylated peptides, applying on-line LC-ion trap MS. ETD MS has so far not been reported for Gla-containing peptides and the applicability of CID for heavily γ-carboxylated proteins has not been evaluated. The anticoagulant protein, protein C, containing nine Gla-sites, was chosen as a model protein. After tryptic digestion, three peptides containing Gla-residues were detected by MS; a 1.2 kDa fragment containing two Gla-residues, a 4.5 kDa peptide containing seven residues and also the 5.6 kDa tryptic peptides containing all nine Gla-residues. Regarding the shortest peptide, both CID and ETD provided extensive peptide sequencing. For the larger peptides, fragmentation by CID resulted in loss of the 44 Da CO(2)-group, while little additional fragmentation of the peptide chain was observed. In contrast, ETD resulted in comprehensive fragmentation of the peptide backbone. The study demonstrates that the combination of both techniques would be beneficial and complementary for investigation of γ-carboxylated proteins and peptides.

Preclinical pharmacology of albumin-free B-domain deleted recombinant factor VIII.

A second-generation recombinant factor VIII molecule was developed with an albumin-free formulation. In this modified form of factor VIII, the N- and C-terminal sections of the B-domain are retained and fused at serine 743 and glutamine 1638, resulting in a B-domain deleted factor VIII protein known as ReFacto (Genetics Institute, Andover, MA). Preclinical studies of ReFacto have focused on efficacy of the product for the hemophilia A patient population. The efficacy and pharmacokinetic profiles of ReFacto were similar to plasma-derived factor VIII in correcting the hemostatic defect of hemophilia A dogs. Both ReFacto and plasma-derived human factor VIII (Octonativ-M7, Pharmacia, Stockholm, Sweden) were found to associate with von Willebrand factor (vWF) after infusion into hemophilia A dogs as demonstrated by size exclusion chromatography. Infusion of either ReFacto or Octonativ-M7 quickly corrected factor VIII coagulant activity (FVIIIc), whole blood clotting time (WBCT), and activated partial thromboplastin time (aPTT). No obvious differences were seen between ReFacto and Octonativ-M7. Both ReFacto and Octonativ-M7 treatment reduced secondary bleeding time to less than 6 minutes. The clearance was faster and the volume of distribution at steady state was larger for plasma-derived factor VIII compared with ReFacto. The half-life was similar between Octonativ-M7 and ReFacto. These data predict that ReFacto will be effective in correcting human factor VIII deficiency states.