Calcium Dependent Properties of Ig 80–83 of N2A Titin

Abstract

Titin is a giant elastic protein responsible for passive force generation in muscles. In addition, numerous studies have implicated a role for titin in active muscle. Recent work on muscles from mdm mice, suggests that during muscle activation, the N2A region of titin binds to actin thereby increasing titin and active muscle stiffness. Atomic force microscopy (AFM) can be used to measure the elastic properties of a titin construct, specifically by unfolding and refolding of its constituent immunoglobulin (Ig) domains. We hypothesized that the Ig domains from the N2A region of titin (Ig 80–83) exhibit different elastic properties in the presence and absence of calcium. To test this hypothesis, we stretched a N2A‐like construct consisting of Ig 80–83 and a Halo‐tag domain at different pulling velocities, in the presence and absence of calcium. Our results suggest a non‐linear unfolding energy landscape for serially linked Ig 80–83 domains in the presence of calcium. We also found, while calcium increased the persistence length of unfolded Ig domains in the N2A‐like construct, its contour length did not change. Increase in persistence length indicates an increase in the stiffness of the N2A domain, which supports the hypothesis that titin stiffness increases in the presence of calcium. These results differ from previous studies without calcium and indicate unique properties of Ig domains specific to the N2A region of titin.Support or Funding InformationAPS IOSP Fellowship Awarded to B. Thompson, NSF IOS‐1451650 Awarded to J. MonroyThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.