S-Glutathionylation of Cryptic Cysteines Enhances Titin Elasticity by Blocking Protein Folding

The giant elastic protein titin is a determinant factor in how much blood fills the left ventricle during diastole and thus in the etiology of heart disease. Titin has been identified as a target of S-glutathionylation, an end product of the nitric-oxide-signaling cascade that increases cardiac muscle elasticity. However, it is unknown how S-glutathionylation may regulate the elasticity of titin and cardiac tissue. Here, we show that mechanical unfolding of titin immunoglobulin (Ig) domains exposes buried cysteine residues, which then can be S-glutathionylated. S-glutathionylation of cryptic cysteines greatly decreases the mechanical stability of the parent Ig domain as well as its ability to fold. Both effects favor a more extensible state of titin. Furthermore, we demonstrate that S-glutathionylation of cryptic cysteines in titin mediates mechanochemical modulation of the elasticity of human cardiomyocytes. We propose that posttranslational modification of cryptic residues is a general mechanism to regulate tissue elasticity. [Display omitted] •Mechanical force exposes cryptic cysteines in titin to allow S-glutathionylation•S-glutathionylation of cryptic cysteines inhibits protein folding•S-glutathionylation of titin reversibly modulates the elasticity of cardiomyocytes•Modification of cryptic cysteines links redox environment to tissue mechanics S-glutathionylation of two cysteines, buried within the folded immunoglobulin domain of titin, modulates its elasticity. The cysteines become exposed when mechanical force unfolds the region, and their modification increases titin elasticity by inhibiting folding.