Molecular characterization of dipeptidyl peptidase activity in serum: Soluble CD26/dipeptidyl peptidase IV is responsible for the release of XâPro dipeptides
2000
Durinx, Christine | Lambeir, AnneâMarie | Bosmans, Eugène | Falmagne, JeanâBernard | Berghmans, Raf | Haemers, Achiel | Scharpé, Simon | De Meester, Ingrid
Dipeptidyl peptidase IV (DPPIV, ECâ3.4.14.5) is a serine type protease with an important modulatory activity on a number of chemokines, neuropeptides and peptide hormones. It is also known as CD26 or adenosine deaminase (ADA; ECâ3.5.4.4) binding protein. DPPIV has been demonstrated on the plasmamembranes of Tâcells and activated natural killer or Bâcells as well as on a number of endothelial and differentiated epithelial cells. A soluble form of CD26/DPPIV has been described in serum. Over the past few years, several related enzymes with similar dipeptidyl peptidase activity have been discovered, raising questions on the molecular origin(s) of serum dipeptidyl peptidase activity. Among them attractin, the human orthologue of the mouse mahogany protein, was postulated to be responsible for the majority of the DPPIVâlike activity in serum. Using ADAâaffinity chromatography, it is shown here that 95% of the serum dipeptidyl peptidase activity is associated with a protein with ADAâbinding properties. The natural protein was purified in milligram quantities, allowing molecular characterization (Nâterminal sequence, glycosylation type, CDâspectrum, pH and thermal stability) and comparison with CD26/DPPIV from other sources. The purified serum enzyme was confirmed as CD26.
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