Mapping the Complement Factor H-Related Protein 1 (CFHR1):C3b/C3d Interactions.
Complement factor H-related protein 1 (CFHR1) is a complement regulator which has been reported to regulate complement by blocking C5 convertase activity and interfering with C5b surface association. CFHR1 also competes with complement factor H (CFH) for binding to C3b, and may act as an antagonist of CFH-directed regulation on cell surfaces. We have employed site-directed mutagenesis in conjunction with ELISA-based and functional assays to isolate the binding interaction that CFHR1 undertakes with complement components C3b and C3d to a single shared interface. The C3b/C3d:CFHR1 interface is identical to that which occurs between the two C-terminal domains (SCR19-20) of CFH and C3b. Moreover, we have been able to corroborate that dimerization of CFHR1 is necessary for this molecule to bind effectively to C3b and C3d, or compete with CFH. Finally, we have established that CFHR1 competes with complement factor H-like protein 1 (CFHL-1) for binding to C3b. CFHL-1 is a CFH gene splice variant, which is almost identical to the N-terminal 7 domains of CFH (SCR1-7). CFHR1, therefore, not only competes with the C-terminus of CFH for binding to C3b, but also sterically blocks the interaction that the N-terminus of CFH undertakes with C3b, and which is required for CFH-regulation.
Department of Medicine, University of Colorado School of Medicine, Aurora, Colorado, United States of America.
Jonathan P
http://orcid.org/0000-0003-3318-2341
JP
Hannan
Department of Medicine, University of Colorado School of Medicine, Aurora, Colorado, United States of America.
Jennifer
J
Laskowski
Department of Medicine, University of Colorado School of Medicine, Aurora, Colorado, United States of America.
Joshua M
JM
Thurman
Sharon Eccles Center for Translational Medicine, John A. Moran Eye Center, Department of Ophthalmology and Visual Sciences, University of Utah, Salt Lake City, Utah, United States of America.
Gregory S
GS
Hageman
Department of Medicine, University of Colorado School of Medicine, Aurora, Colorado, United States of America.
V Michael
VM
Holers
D001665:Binding Sites / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D050577:Complement C3-C5 Convertases / Q000378:metabolism; D003179:Complement C3b / Q000378:metabolism*; D003180:Complement C3b Inactivator Proteins / Q000378:metabolism*; D015933:Complement C3d / Q000378:metabolism*; D003165:Complement System Proteins / Q000378:metabolism*; D006801:Humans; D016297:Mutagenesis, Site-Directed / Q000379:methods
C517621:CFHR1 protein, human; D003180:Complement C3b Inactivator Proteins; D003179:Complement C3b; D015933:Complement C3d; D003165:Complement System Proteins; D050577:Complement C3-C5 Convertases