Characterization of the native C-reactive protein (cCRP) and the corresponding liver mRNA in dogs.

C-reactive protein (CRP) plays an important role in the acute phase reaction in humans and dogs. For the canine CRP (cCRP) only an in silico deduced preliminary transcript and amino acid sequence is available. The objective of this study was to further characterize the native cCRP protein and its corresponding liver mRNA. Furthermore, immunological similarities of serum CRP in related animal species were investigated. Native cCRP protein was isolated from dog-sera by affinity chromatography and further analyzed by immunodetection, protein sequencing (mass spectrometry and N-terminal Edman sequencing), 2D-gel electrophoresis, and glycoprotein analysis. Furthermore, cCRP cDNA sequence was determined from dog liver total RNA by RT-PCR. Gel electrophoresis, immunodetection and glycoprotein detection revealed two cCRP isotypes with different molecular weights (22 and 25kDa) with the upper band being glycosylated. Selective glycoprotein analysis showed sialic acid terminally linked (2-6) to galactose or N-acetylgalactosamine and subsequent PNGase F treatment identified N-terminal linkage. Mass spectrometry confirmed approximately 45% of the cCRP predicted amino acid sequence and N-terminal amino acid sequencing revealed a shorter native cCRP than expected (204 amino acids). The new canine CRP mRNA sequence confirms 100% of the formerly deduced sequence. Immunological homologies to the canine CRP protein were found in selected dog-related species. This study contributes major molecular details to the knowledge about canine CRP. Such structural information may assist in developing new diagnostic tools for inflammatory-based diseases in dogs as well as other dog-related species.