Mapping of the domains required for decay acceleration activity of the human factor H-like protein 1 and factor H.
The human factor H-like protein 1 (FHL-1) is composed of seven repetitive elements (short consensus repeats; SCR) that are identical in sequence to the seven N-terminal SCR of complement factor H. We show that the FHL-1 protein has decay acceleration activity in that it can dissociate C3/C5-convertases bound to the surface of sheep red blood cells. The same activity was also determined for factor H. However, compared to FHL-1, factor H was more efficient in decay acceleration, as about 100-fold less protein was required for a 50% inhibition of activity. The domain required for decay accelerating activity of FHL-1 and factor H was mapped by the use of recombinant fragments. FHL-1 and a series of truncated forms of the protein were expressed in the baculovirus system. Recombinant FHL-1 and all mutants which include SCR 1-4 were functionally active. These four N-terminal SCR are essential and sufficient for activity, as deletion mutants which lack SCR 1 or SCR 4 showed no activity. These results demonstrate that FHL-1 and factor H have identical and overlapping regulatory functions in the complement system and that the domain required for this activity is located in the overlapping region of both proteins within the N-terminal four SCR.
Department of Molecular Biology, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany.
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D000818:Animals; D001798:Blood Proteins / Q000737:chemistry*; D002478:Cells, Cultured; D003176:Complement C3 / Q000378:metabolism; D050577:Complement C3-C5 Convertases / Q000378:metabolism; D003179:Complement C3b / Q000378:metabolism; D017242:Complement Factor H / Q000737:chemistry*; D003170:Complement Pathway, Alternative; D004910:Erythrocyte Membrane / Q000378:metabolism; D006801:Humans; D010446:Peptide Fragments / Q000378:metabolism; D011485:Protein Binding; D011994:Recombinant Proteins; D012756:Sheep; D013329:Structure-Activity Relationship
D001798:Blood Proteins; C493495:CFH protein, human; D003176:Complement C3; D010446:Peptide Fragments; D011994:Recombinant Proteins; C100631:factor H-related protein 1; D003179:Complement C3b; D017242:Complement Factor H; D050577:Complement C3-C5 Convertases