Circular dichroism analysis of a synthetic peptide corresponding to the alpha, alpha-corner motif of hemoglobin.

The alpha, alpha-corner is a helix-turn-helix super-secondary structural protein motif where the two alpha-helices cross at approximately right angles. This motif has been observed in a wide variety of proteins and thus, has been proposed to be a protein folding initiator. We sought to test this hypothesis by synthesizing a peptide corresponding to the alpha, alpha-corner of the alpha-chain of horse methemoglobin (residues 80-108) and examining its structure by circular dichroism. We found that the alpha, alpha-corner peptide is moderately helical in water and fully helical in trifluoroethanol, as solvent that approximates the hydrophobic surroundings of the excised portion of the protein. The helicity of our synthetic peptide suggests that the alpha, alpha-corner may in fact have some stability on its own and thus, may be capable of initiating protein folding.