ANTIFREEZE PEPTIDE HETEROGENEITY IN AN ANTARCTIC EEL POUT INCLUDES ANUNUSUALLY LARGE MAJOR VARIANT COMPRISED OF 2 7-KDA TYPE-III AFPS LINKED IN TANDEM

The structural heterogeneity of the major antifreeze peptides (AFPs) f rom the antarctic eel pout, Lycodichthys dearborni (formerly classifie d as Rhigophila dearborni) was characterized. Three major AFPs designa ted as RD1, RD2 and RD3, and five minor ones were isolated from the fi sh plasma. RD1 and RD2 are both 64 residues in length, about 7 kDa, an d thus similar in size to all characterized type III AFPs, while RD3 i s twice as large, about 14 kDa, and represents the first example of a disparately large size variant within the same fish for the three know n types of antifreeze peptides. RD3 was found to be 134 residues in le ngth, arranged as a 64-residue N-terminal half and a 61-residue C-term inal half of similar sequence to each other and to the 7 kDa type III AFPs, linked by a 9-residue connector of unmatched sequence. RD3 has s lightly lower antifreeze activity than its 7 kDa counterparts, with a melting-freezing point difference of about 0.81 degrees C at 10 mg/ml versus 0.95 degrees C and 0.90 degrees C for RD1 and RD2, respectively . RD1 and RD2 are 94% identical in sequence to each other. They are 98 % and 94%, respectively identical to N-terninal half of RD3, and 85% a nd 77%, respectively, identical to C-terminal half of RD3. By sequence comparison, a previously characterized AFP from this fish [1] was ide ntified to be RD2.