ISOLATION AND CHARACTERIZATION OF AN ANTIFREEZE PROTEIN FROM THE LONGHORN SCULPIN, MYOXOCEPHALUS-OCTODECIMSPINOSIS

A new type of antifreeze protein was isolated from the serum of the lo nghorn sculpin, Myoxocephalus octodecimspinosis, by gel filtration and high-performance liquid chromatography. This protein (LS-12) exhibits freezing point depression activity (thermal hysteresis) and ice cryst al modification properties similar to those seen for other types of fi sh antifreeze polypeptide, except that ice crystals grow as hexagonal trapezohedra in the presence of LS-12, rather than hexagonal bipyramid s usually seen. Ice crystal etching studies demonstrate that LS-12 doe s not bind to the hexagonal bipyramidal or secondary prism surfaces re ported for the antifreeze polypeptides from winter flounder and shorth orn sculpin, respectively. Circular dichroism studies indicate that LS -12 has an a-helix content of about 60% at 1 degrees C, which is in go od agreement with a value of about 70% predicted from the amino acid s equence. Limited proteolysis studies and further analysis of the amino acid sequence suggest that LS-12 consists of four amphipathic a-helic es of similar length which are folded into a four-helix bundle. Based on its size (M-r = 12299) and predicted tertiary structure, LS-12 can be regarded as the first example of a new class (type IV)? of fish ant ifreeze protein. (C) 1998 Elsevier Science B.V. All rights reserved.