Stretching the α-helix: a direct measure of the hydrogen-bond energy of a single-peptide molecule

Abstract Atomic force microscopy was used to measure the force required to stretch individual molecules of the peptide cysteine 3 –lysine 30 –cysteine from the α-helical state into a linear chain (approximately 200 pN). The measured force versus peptide elongation was used to calculate the work done in breaking the hydrogen bonds which give rise to the helical structure. The average experimental value of the hydrogen-bond energy (20.2 kJ/mol) is in good agreement with reported theoretical calculations. In addition, the stiffness of individual peptides was measured directly using a force modulation technique and found to vary from approximately 0.005–0.012 N/m during elongation.

[1]  A. Oral,et al.  A novel force microscope and point contact probe , 1993 .

[2]  J. Israelachvili.  Intermolecular and surface forces , 1985 .

[3]  A. Ikai,et al.  Mechanical unfolding of a2‐macroglobulin molecules with atomic force microscope , 1996 .

[4]  Andres F. Oberhauser,et al.  The molecular elasticity of the extracellular matrix protein tenascin , 1998, Nature.

[5]  S. Smith,et al.  Folding-unfolding transitions in single titin molecules characterized with laser tweezers. , 1997, Science.

[6]  R. M. Simmons,et al.  Elasticity and unfolding of single molecules of the giant muscle protein titin , 1997, Nature.

[7]  M. Welland,et al.  Atomic force microscopy of local compliance at solid—liquid interfaces , 1994 .

[8]  P. Haris,et al.  The conformational analysis of peptides using fourier transform IR spectroscopy , 1995, Biopolymers.

[9]  Gil U. Lee,et al.  Direct measurement of the forces between complementary strands of DNA. , 1994, Science.

[10]  David A. Dixon,et al.  Amide-Water and Amide-Amide Hydrogen Bond Strengths , 1994 .

[11]  Matthias Rief,et al.  Single Molecule Force Spectroscopy on Polysaccharides by Atomic Force Microscopy , 1997, Science.

[12]  S. Lee,et al.  Design and synthesis of amphiphilic alpha-helical model peptides with systematically varied hydrophobic-hydrophilic balance and their interaction with lipid- and bio-membranes. , 1996, Biochemistry.

[13]  M. Rief,et al.  Reversible unfolding of individual titin immunoglobulin domains by AFM. , 1997, Science.