ATYPICAL PHOSPHORYLCHOLINE-REACTIVE PROTEIN FROM ATLANTIC SALMON, SALMO-SALAR L

A phosphorylcholine-reactive protein was isolated from serum of Atlant ic salmon (Salmo salar, L.) by affinity chromatography on a phosphoryl choline-conjugated Sepharose column followed by elution with phosphory lcholine. Based on the method used we describe the isolated protein as salmon phosphorylcholine-reactive protein (salmon PRP). Salmon PRP ha s calcium-independent binding to phosphorylcholine. The protein exists in a monomeric and dimeric form with molecular weight of approximatel y 80 and 160 kD, respectively. Separation of the protein preparation o n SDS-PAGE under reducing conditions resulted in disappearance of the 80 and 160 kD bands and appearance of a major protein band of approxim ately 100 kD. The N-terminal amino acid sequences of the non-reduced 8 0 and 160 kD bands and the reduced 100 kD band were identical. Apart f rom the dimeric form, the molecular weight of salmon PRP and its appea rance on SDS-PAGE is similar to human plasminogen. Comparison of the s equence in a protein database resulted in approximately 50% identity w ith human and bovine plasminogen. In addition, cross-reactivity betwee n antibodies to human plasminogen and salmon PRP was demonstrated. Thu s, salmon PRP appears to be different from other phosphorylcholine-rea ctive proteins which are mostly reported to be CRP-like proteins with calcium-dependent binding to phosphorylcholine, pentameric ring-struct ure 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 phosphorylcho line calls for further investigation. (C) 1998 Elsevier Science Inc. A ll rights reserved.