The invention relates to a polypeptide capable of binding human complement component 5 (C5), said polypeptide comprising the amino acid sequence [BM]-[L2]-QSX42X43LLX46EAKKLX52X53X54Q wherein [BM] is a C5 bindingmotif; [L2] is an interconnecting loop; X42 is selected from A and S; X43 is selected from N and E; X46 is selected from A, S and C; X52 is selected from E, N and S; X53 is selected from D, E and S, provided that X53 is not D when X52 is N; and X54 is selected from A and S.