A psychrophilic yeast was isolated from an Arctic pond and its culture supernatant
showed ice-binding activity. This isolate, identified as Leucosporidium sp. based
on an analysis of the D1/D2 and ITS regions of its ribosomal DNA, produced a secretory
ice-binding protein (IBP). Yeast IBP was purified from the culture medium to near
homogeneity by the ice affinity method and appeared to be glycosylated with a molecular
mass of approximately 26 kDa. In addition, the yeast IBP was shown to have thermal
hysteresis (TH) and recrystallization inhibition (RI) activities. The full-length
cDNA for yeast IBP was determined and was found to encode a 261 amino acid protein
with molecular weight of 26.8 kDa that includes an N-terminal signal peptide and one
potential N-glycosylation site. The deduced protein showed high sequence identity
with other IBPs and hypothetical IBPs from fungi, diatoms, and bacteria, clustering
with a class of ice-active proteins.
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