A variant of the C-terminal Kunitz-type protease inhibitor domain of the α3 chain of human type VI collagen, the variant comprising the amino acid sequence (I) wherein X1 represents H or 1-5 naturally occurring amino acid residues except Cys, X2-X14 each independently represents a naturally occurring amino acid residue, and X15 represents OH or 1-5 naturally occurring amino acid residues except Cys, with the proviso that at least one of the amino acid residues X1-X15 is different from the corresponding amino acid residue of the native sequence.