Disclosed is a polypeptide consisting of: (i) an amino acid sequence having at least 90% identity to an amino acid sequence set forth in SEQ ID NO:4 or (ii) an amino acid having at least 90% identity to an amino acid sequence set forth in SEQ ID NO:8. Further disclosed is a polypeptide consisting of an amino acid sequence: A{ XL} nB wherein: each X is a polypeptide as defined above L is an optional linker amino acid sequence A is an optional N terminal amino acid sequence B is an optional C terminal amino acid sequence and n is an integer of 1 or more.