Conformational properties of five peptides corresponding to the entire sequence of glutathione transferase domain II

Five peptides matching the helices alpha4, alpha5, alpha6, alpha7, and alph a8, spanning the entire sequence of domain II of pGSTP1-1, have been synthe sized and their conformations analyzed by far-UV CD spectroscopy. The resul ts show that a5, a7, and a8 peptides are unstructured in water/2,2,2-triflu oroethanol (TFE) solutions. The a4-peptide also adopts random conformations in aqueous solvent. Moreover, the relative low helical content (20%), esti mated for this peptide in the presence of 30% (v/v) TFE, suggests that the sequence of this protein fragment does not possess sufficient information f or a strong helical propensity. On the contrary, the synthesized a6 peptide , in the presence of TFE, showed a relevant structural autonomy with a heli cal content (41%) which was significantly higher than that estimated, under the same conditions, for all other peptides. More in general in the presen ce of solvents less polar than water, the isolated a6 peptide shows the sam e helical conformation adopted by the corresponding alpha6-helix in the hyd rophobic core of the protein, A n-capping box motif, strictly conserved at the N-terminal of the alpha6-helix of all GST and related protein including eucaryotic translation elongation factor (EF1 gamma) and the yeast prion p rotein Ure2, plays an important role in the alpha -helix nucleation and sta bility of this protein fragment. The results suggest that the alpha6-helix might represent a nucleation site of GST folding and that the helical confo rmation of this region of the protein is an important requirement during ea rlier events of GST refolding. (C) 2001 Academic Press.