Augusto Guggi

Conformational transition of the synthetic 2-15 N-terminal fragment of hen egg-white lysozyme.

It has been proposed [ 1 ] that the folding of a protein molecule begins at the amino end even before the synthesis is complete. Such a sequential mechanism presumes that the protei’n conformation is primarily due to interactions between amino acid residues close in the sequence and implies that parts of the polypeptide chain, particularly those near the terminal amino end, may fold into stable conformations that can still be recognized in the complete molecule and act as ‘internal templates’ around which the rest of the chain is folded. The results obtained by studying the conformational properties of the N-terminal eicosapeptide (S-peptide) [2, 31 of bovine pancreatic ribonuclease and of several S-peptide synthetic analogs [4] in aqueous solution and in the presence of helicogenic solvent, do not agree with the hypothetical sequential mechanism mentioned above. The hen egg-white lysozyme was shown by X-ray analysis [5] to contain three runs of helix (residues 515,24-34 and 88-96) for which the axial translation per residue and the number of residues per turn fall close to the a-helix values. The aim of the present paper is to report some preliminary conformational studies on the synthetic tetradecapeptide corresponding to the 2-l 5 N-terminal fragment of hen egg-white lysozyme. The peptide conformation has been investigated by circular dichroism in aqueous solution and in the presence of trifluoroethanol which is known to cause a transition from the random to the helical form in polypeptide systems.