SYNTHESIS AND CHARACTERIZATION OF A FRAGMENT OF AN ICE NUCLEATION PROTEIN

Synthetic peptides were used as models for studying the conformation o f ice nucleation proteins. We chemically synthesized four peptides (16 -, 24-, 32-, and 48-mer) that consisted of two to six repeats of the c onsensus repeating octapeptide unit of ice nucleation proteins and eva luated their conformation by circular dichroism spectroscopy. These mo del peptides exist predominantly as random coils in aqueous solution, but adopt alpha-helical structures in the presence of trifluoroethanol . The stability of their secondary structures was investigated by moni toring the pH and time of their circular dichroism spectra. Our result s indicated that the alpha-helical content of the 48-mer exhibited a s ignificant pH dependence, while that of the 24- and 32-mer peptides di d not. The 32-mer was the only peptide that transformed from the alpha -helical to beta-sheet structure upon storage. We suggest that the ove rall conformation of the ice nucleation protein could be a beta-sheet.