Assessment of the Functional Role of the NTR Domain of Complement Component C3 using a Homologous Dmain Exchange Approach

• Main Author: Rana, Amardeep
• Other Authors: Isenman, David
• Language: en_ca
• Published: 2010
• Subjects: Complement; NTR; C345C; C3; C5; Complement Receptor 1; factor H; factor B; 0487
• Online Access: http://hdl.handle.net/1807/25901

The complement system plays an important role in innate and adaptive immunity. Central to all complement activities is the function of complement component 3 (C3). C3 contains a C-terminal extension of ~150 residues known as the NTR (or C345C) domain. To address the role of the NTR domain in binding and functional activities of C3, a C3/C5 chimera was engineered, in which the NTR domain of C3 was replaced by the homologous domain of the closely related protein C5. Functionally, the C3(C5NTR) was devoid of classical pathway-dependent hemolytic activity and deficient in factor H- and CR1-dependent factor I cleavability. Direct binding SPR assays, using chip bound methylamine treated His6-tagged C3(C5NTR), showed a complete loss of C5 binding while retaining wild type binding with CR1, factor H and factor B. These results present the first evidence for a major C5 binding site within C3 NTR.