Expression, purification, and functional characterization of a Kunitz-type module from chicken type VI collagen

The primary amino acid sequence of the carboxyl-terminal portion of the α3 chain of chicken type VI collagen (K-VI) presents a 58-residue motif with a high degree of homology with members of the Kunitz serine-proteinase inhibitors family. This module was cloned, expressed in E. coli, purified and compared to the bovine pancreatic trypsin inhibitor (BPTI) in an inhibition profile assay of two serine proteases, trypsin and plasmin. We found that recombinant K-VI is not endowed with inhibitory activity but it slightly activates both plasmin and trypsin, differently from other members of the family. Moreover, the ability to inhibit the serine protease activity is also lacking in the intact type VI collagen molecule.