| 摘要 |
Polypeptides are disclosed that are capable of being isolated from ectoparasitic leeches which inhibit the alternative route of complement activation but which have substantially no effect on complement activation by the classical route. In one embodiment of the invention, the polypeptides have the following general formula [SEQ ID NO: 50] in which amino acids are represented by their conventional single letter codes: X1-E-F-Q-D-X2-K-K-S-S-D-X3-E-T-L-E-L-R-X4-N-K-X5, wherein: X1 is a hydrogen atom (H) or any naturally-occurring amino acid, preferably valine, or a sequence of amino acids; X2 is any single amino acid, preferably cysteine; X3 is any single amino acid, preferably cysteine; X4 is any single amino acid, preferably cysteine; X5 is an amino acid sequence comprising naturally-occurring amino acids, one or more of which may comprise post-translational modifications, such as glycosylation at asparagine, serine or threonine; and/or sulphato- or phospho- groups on tyrosine, such as are commonly found in polypeptides derived from leeches. The polypeptides can be prepared from leech species of the order Rhynchobdellida and more particularly those of the genus Placobdella, especially of the species Placobdella papillifera. Alternatively, the polypeptides can be synthesised chemically or produced by transgenic organisms carrying DNA sequences which encode them. Accordingly, also disclosed are nucleic acid sequences capable of expressing the polypeptides; hosts, and vectors comprising these sequences; and the use of the nucleic acids and polypeptides in therapy. |
