TCB Publications - Abstract

Hui Lu, Barry Isralewitz, André Krammer, Viola Vogel, and Klaus Schulten. Unfolding of titin immunoglobulin domains by steered molecular dynamics simulation. Biophysical Journal, 75:662-671, 1998.

LU98 Titin, a 1 $\mu$m long protein found in striated muscle myofibrils, possesses unique elastic and extensibility properties in its I-band region, which is largely composed of 7-strand $\beta$-sandwich immunoglobulin-like (Ig) domains. The behavior of titin as a hysteretical, multi-stage entropic spring has been shown in atomic force microscope and optical tweezer experiments to depend on the reversible unfolding of individual Ig domains. We performed steered molecular dynamics simulations to stretch single titin Ig domains in solution with pulling speeds of 0.5 and 1.0 $\AA$/ps. Resulting force-extension profiles exhibit a single dominant peak for each Ig domain unfolding, consistent with the experimentally observed sequential, as opposed to concerted, unfolding of Ig domains. This force peak can be attributed to an initial burst of backbone hydrogen bonds, which takes place between $\beta$-strands A and B in between $\beta$-strands A' and G. Additional features of the simulations, including the position of the force peak and relative unfolding resistance of different Ig domains, can be related to experimental observations.

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