Atypical phosphorylcholine-reactive protein from Atlantic salmon, Salmo salar L.
A phosphorylcholine-reactive protein was isolated from serum of Atlantic salmon (Salmo salar L.) by affinity chromatography on a phosphorylcholine-conjugated Sepharose column followed by elution with phosphorylcholine. Based on the method used we describe the isolated protein as salmon phosphorylcholine-reactive protein (salmon PRP). Salmon PRP has calcium-independent binding to phosphorylcholine. The protein exists in a monomeric and dimeric form with molecular weight of approximately 80 and 160 kD, respectively. Separation of the protein preparation on SDS-PAGE under reducing conditions resulted in disappearance of the 80 and 160 kD bands and appearance of a major protein band of approximately 100 kD. The N-terminal amino acid sequences of the non-reduced 80 and 160 kD bands and the reduced 100 kD band were identical. Apart from the dimeric form, the molecular weight of salmon PRP and its appearance on SDS-PAGE is similar to human plasminogen. Comparison of the sequence in a protein database resulted in approximately 50% identity with human and bovine plasminogen. In addition, cross-reactivity between antibodies to human plasminogen and salmon PRP was demonstrated. Thus, salmon PRP appears to be different from other phosphorylcholine-reactive proteins which are mostly reported to be CRP-like proteins with calcium-dependent binding to phosphorylcholine, pentameric ring-structure and sequence homology between species. Whether salmon PRP is a new type of phosphorylcholine-binding protein with an unknown function or a plasminogen-like protein with binding specificity for phosphorylcholine calls for further investigation.
Lund
V
V
Department of Marine Biochemistry, Norwegian College of Fishery Science, University of Tromsø, Norway. veral@nfh.uit.no
Olafsen
J A
JA
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002097:C-Reactive Protein / Q000032:analysis* / Q000737:chemistry* / Q000302:isolation & purification; D002417:Cattle; D002846:Chromatography, Affinity; D003429:Cross Reactions; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010767:Phosphorylcholine / Q000378:metabolism; D010958:Plasminogen / Q000737:chemistry; D012474:Salmon; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D010767:Phosphorylcholine; D010958:Plasminogen; D002097:C-Reactive Protein