Mechanically weak and highly dynamic state of mechanosensitive titin Ig domains induced by proline isomerization
Yukai Wang, Jiaqing Ye, Xian Liu, Zhuwei Zhang, Fei Shang, Xingyu Qi, Y. N. Zhang, Jingyi Du, Hao Sun, Jiashu Xu, Hu Chen, Miao Yu, Shimin Le
Abstract
Titin, essential for mechano-homeostasis in cardiac and skeletal sarcomere, contains numerous mechanosensitive immunoglobulin-like (Ig) domains in its I-band region. However, how proline isomerization and cysteine-mediated disulfide bond collectively regulate Ig domain dynamics within the physiological force range remains unclear. Here, we use single-molecule force spectroscopy to quantify the proximal Ig1 domain, revealing that proline isomerization leads to two native states–trans and cis states–with distinct mechanical and thermal stabilities. The trans-Ig1 unfolds at forces of ~ 5 pN, which is over 50 pN lower than that of cis-Ig1, and unfolds 1000 times faster under physiological forces. Furthermore, such proline induced dual-state is likely shared feature across majority of I-band Ig domains. Additionally, reduced cis- and trans-Ig1 exhibit catch-slip bond unfolding, while oxidized forms display slip-catch-slip unfolding. This study offers insight into effective modulation of proline isomerization and disulfide bond in regulating mechanosensitive proteins within the physiological force range. Using single-molecule force spectroscopy, the authors demonstrate that proline isomerization and cysteine-mediated disulfide bonds lead to distinct mechanical states of the titin I-band immunoglobulin-like domains within the physiological force range.