Primary structures of the alanine-rich antifreeze polypeptides from grubby sculpin, Myoxocephalus aenaeus

Abstract

Antifreeze polypeptides (AFP) isolated from the plasma of the grubby sculpin (Myoxocephalus aenaeus)were compared with those of a close relative, the shorthorn sculpin (Myoxocephalus scorpius). Both species synthesize a family of AFP that are alanine rich and exist as amphiphilic α-helices. The grubby sculpin AFP could be resolved into five active components by reverse-phase liquid chromatography. The major (GS-5) and one of the minor (GS-8) components were sequenced. Grubby sculpin AFP GS-5 was 33 amino acids long. It was homologous to one of the minor shorthorn sculpin AFP (SS-3) in terms of its molecular size and amino acid sequence. The sequences of these two components differed by only four amino acids. The minor grubby sculpin AFP GS-8 was 40 amino acids long. It was shorter than the major shorthorn sculpin AFP (SS-8) by five amino acids. The sequence of the first 40 amino acids from SS-8 and GS-8 was essentially identical, differing by only 4 amino acids. Antibodies raised against SS-8 cross reacted with GS-8 but not with the shorter AFP (GS-5 and SS-3). The data suggest that the antibody was directed towards the unstructured N-terminal regions of SS-8 and GS-8. It would appear that shorthorn and grubby sculpins possess similar families of AFP genes and that the grubby sculpin preferentially expresses one gene product (GS-5) while the shorthorn sculpin expresses another, larger product (SS-8).