Purification and characterization of an insect hemolymph lipoprotein ice nucleator: evidence for the importance of phosphatidylinositol and apolipoprotein in the ice nucleator activity

A lipoprotein with ice nucleator activity was purified from the hemolymph of the freeze-tolerant larvae of the cranefly Tipula trivittata . Characterization of this lipoprotein ice nucleator (LPIN) showed that it differed from other previously described insect hemolymph lipoproteins which lack ice nucleator activity, by the presence of phosphatidylinositol (PI) at 11.0% by weight of the total phospholipid content. The potential roles of PI and other lipoprotein components in the ice nucleating activity were examined using various phospholipases, proteases, LPIN antibodies, borate compounds and various lipid-protein reconstitutions.