Characterization of C-reactive protein and the complement subcomponent C1t as homologous proteins displaying cyclic pentameric symmetry (pentraxins).

Abstract
Partial amino acid sequences of rabbit C-reactive protein [CRP], a peptide derived from human CrP by CNBr cleavage, and human C1t[t subcomponent of the 1st complement component] were determined. Extensive sequence homology between these proteins establish their evolutionary relationships. Examination of C-reactive proteins by negative-stain EM revealed that the protein is composed of 5 subunits arranged in cyclic symmetry. This structure is similar to C1t and the amyloid P-component. The extensive structural relationship suggests similar or overlapping functions, and the term pentraxin is proposed to describe these homologous proteins.