Measurement of the Length of the α Helical Section of a Peptide Directly Using Atomic Force Microscopy

Abstract

Using atomic force microscopy (AFM), the length of the α-helix structure of poly-L-lysine was investigated by stretching the peptide directly, one molecule at a time. In the absence of urea, many rupturing points that seemed to be due to the breaking of some hydrogen bonds were observed in force-extension curves, while these points were never observed in the presence of 8 M urea. In the presence of 0.4 or 1.6 M urea, both force-extension curve types were observed. Total peptide elongation for each condition was calculated from force-extension curves reflecting the α-helix rupturing process. The experimental value of total elongation divided by the theoretical value of total α-helix elongation yields the α-helix content. This value was compatible with circular dichroism (CD) measurement results. This suggests that peptide conformation and content of the α-helix on a single molecule scale can be investigated by direct mechanical measurement using atomic force microscopy.