Extending a Spectrin Repeat Unit. I: Linear Force-Extension Response

Nonequilibrium molecular dynamics simulations were used to calculate the elastic properties of a spectrin repeat unit. A contiguous α-helical linker was constructed by employing periodic boundary conditions, allowing a novel scheme for evaluating the thermodynamic force as a function of extension. By measuring the force-extension response under small extensions, spectrin was observed to behave primarily as an elastic material with a spring constant of 1700 ± 100 pN/nm. The implications of this spring constant, in terms of the properties of the spectrin tetramer, are also discussed.