Circular Dichroism Analysis of a Synthetic Peptide Corresponding to the α,α-Corner Motif of Hemoglobin

The α,α-corner is a helix-turn-helix super-secondary structural protein motif where the two α-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 α,α-corner of the α-chain of horse methemoglobin (residues 80-108) and examining its structure by circular dichroism. We found that the α,α-corner peptide is moderately helical in water and fully helical in trifluoroethanol, a solvent that approximates the hydrophobic surroundings of the excised portion of the protein. The helicity of our synthetic peptide suggests that the α,α-corner may infact have some stability on its own and thus, may be capable of initiating protein folding.