Apolipoprotein CII from rainbow trout (Oncorhynchus mykiss) is functionally active but structurally very different from mammalian apolipoprotein CII

Apolipoprotein CII (apoCII) plays an important role in plasma lipid metabol ism as an activator for lipoprotein lipase (LPL). We have amplified and seq uenced apoCII cDNA from rainbow trout. Amino acid sequence analyses confirm ed that this sequence corresponded to the protein that had apoCII activity. Northern blot analyses showed that apoCII mRNA was present in both liver a nd intestine, but the level in intestine was very low. Two major transcript s (800 and 600 bp) were found. The predicted amino acid sequence consists o f 112 amino acid residues, including the signal peptide. The mature peptide is seven residues longer than human apoCII (86 versus 79 residues) due to an extension at the amino-terminal end. The rainbow trout sequence showed a n overall identity of only 20-25% to previously known apoCII sequences. The carboxy-terminal region (residues 51-79, human numbering) showed 35-45% id entity to other apoCII sequences, while in the amino-terminal region, there was little if any identity and it was not possible to predict any long amp hipathic, potentially lipid-binding alpha-helices. Trout apoCII was present in all lipoprotein fractions including LDL. At +10 degrees C trout plasma showed higher ability to stimulate LPL than human plasma. We conclude that apoCII from rainbow trout is in most parts structurally different from apoC II from other species, and that it is adapted to function at low temperatur e. (C) 2000 Published by Elsevier Science B.V. All rights reserved.