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

Atomic force microscopy was used to measure the force required to stretch i ndividual molecules of the peptide cysteine(3)-lysine(30)-cysteine from the alpha-helical state into a linear chain (approximately 200 pN). The measur ed force versus peptide elongation was used to calculate the work done in b reaking the hydrogen bonds which give rise to the helical structure. The av erage experimental value of the hydrogen-bond energy (20.2 kJ/mol) is in go od agreement with reported theoretical calculations. In addition, the stiff ness of individual peptides was measured directly using a force modulation technique and found to vary from approximately 0.005-0.012 N/m during elong ation. (C) 1999 Elsevier Science B.V. All rights reserved.