VALINE SUBSTITUTED WINTER FLOUNDER ANTIFREEZE - PRESERVATION OF ICE GROWTH HYSTERESIS

Three mutant polypeptides of the type I 37-residue winter flounder 'an tifreeze' protein have been synthesized. All four threonine residues i n the native peptide were been mutated to serine, valine and glycine r espectively and two additional salt bridges were incorporated into the sequences in order to improve aqueous solubility, The peptides were a nalyzed by nanoliter osmometry, the 'ice hemisphere' test, the 'crysta l habit' test, measurement of ice growth hysteresis and CD spectroscop y. White the valine and serine mutants retain the a-helical structure, only the valine mutant retains 'antifreeze' activity similar to that of the native protein. These data show that the threonine hydroxyl gro ups do not play a crucial role in the accumulation of the native 'anti freeze' protein at the ice/water interface and the inhibition of ice g rowth below the equilibrium melting temperature. (C) 1998 Federation o f European Biochemical Societies.