title: Nonlinear elasticity of an alpha -helical polypeptide.
abstract: We study a minimal extension of the wormlike chain model to describe polypeptides having alpha-helical secondary structure. In this model the presence or absence of secondary structure enters as a scalar variable that controls the local chain bending modulus. Using this model we compute the extensional compliance of an alpha-helix under tensile stress, the bending compliance of the molecule under externally imposed torques, and the nonlinear interaction of such torques and forces on the molecule. We find that, due to coupling of the "internal" secondary structure variables to the conformational degrees of freedom of the polymer, the molecule has a highly nonlinear response to applied stress and force couples. In particular we demonstrate a sharp lengthening transition under applied force and a buckling transition under applied torque. Finally, we speculate that the inherent bistability of the molecule may underlie protein conformational change in vivo.
authors.affiliation: Department of Physics, University of Massachusetts, Amherst, 01003, USA. buddho@physics.umass.edu
authors.forename: Buddhapriya
authors.initials: B
authors.lastname: Chakrabarti
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Levine
mesh_terms: D003198:Computer Simulation; D004548:Elasticity; D008846:Micromanipulation / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D017711:Nonlinear Dynamics; D010455:Peptides / Q000737:chemistry*; D010812:Physical Stimulation / Q000379:methods*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013314:Stress, Mechanical
chemical_list: D010455:Peptides