MOLECULAR CHARACTERIZATION AND SEQUENCING OF ANTIFREEZE PROTEINS FROMLARVAE OF THE BEETLE DENDROIDES CANADENSIS

The deduced amino acid sequences of antifreeze proteins (AFPs) from la rvae of the beetle Dendroides canadensis were determined from both com plementary DNAs (cDNAs) and from peptide sequencing. These consisted o f proteins with a 25-residue signal peptide and mature proteins 83 (De ndroides antifreeze protein; DAFP-1) or 84 (DAFP-2) amino acids in len gth which differed at only two positions. Peptide sequencing yielded s equences which overlapped exactly with those of the deduced cDNA seque nces of DAFF-1 and DAFP-2, while the partial sequence of another AFP ( DAFP-3) matched 21 of 28 residues. Seven 12- or 13-mer repeating units are present in these antifreeze proteins with a consensus sequence co nsisting of: Thr-X-3-Ser-X-5-X-6-Cys-X-8-X-9-Ala-X-11-Thr-X-13, where X-3 and X-11 tend toward charged residues, X-5 tends toward threonine or serine, X-6 toward asparagine or aspartate, X-9 toward asparagine o r lysine, and X-13 toward alanine in the 13-mers. The most interesting feature of these proteins is that throughout the length of the mature antifreeze proteins every sixth residue is a cysteine. These sequence s are not similar to any of the known fish AFPs, but they are similar to AFPs from the beetle Tenebrio molitor.