Localisation of the C1q binding site within C 1 q receptor/calreticulin

Clq receptor (C1gR/collectin receptor) is located on many cell types. Binding of C1q to these cells elicits numerous responses. Protein sequencing has shown that C1gR is almost identical to calreticulin (CaR), an abundant multifunctional protein. Radioiodinated C1gR and CaR bind to C1q with identical characteristics. Three recombinant C1gR/CaR domains (N‐, C‐terminal domains and central P‐domain) were expressed using the Thiofusion system, and used to study the interaction with C1q. Both the N‐ and P‐domains were implicated in C1q binding. A region, termed the S‐domain, spanning the N and P intersection was expressed, and showed concentration‐dependent binding to C1q, demonstrating that the Clq binding site lies within this region.

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