A comparative study of pentraxin-like proteins in different fish species.

Pentraxins are a family of pentameric serum proteins that have been conserved in evolution and share sequence homology, similar subunit assembly and the capacity for calcium-dependent ligand binding. The classical pentraxins are human C-reactive protein (CRP) and serum amyloid P component (SAP). The sequence homology and gene organization indicate that they arose from a gene duplication of an ancestral pentraxin gene. They are usually isolated based on their affinity for phosphorylcholine and agarose, respectively. We have used this method for isolation of pentraxin-like proteins from normal serum of Atlantic salmon (Salmo salar), common wolffish (Anarhichas lupus), cod (Gadus morhua) and halibut (Hippoglossus hippoglossus). Although pentraxin structures have not been verified, the isolated proteins all appear to be pentraxin-like based on their binding specificity, molecular weight of subunits, cross-reactivity with antibodies to human pentraxins and N-terminal amino acid sequences. However, with the described method only one pentraxin-like protein was detected in each of the fish species.