Folding and\nMisfolding Dynamics of Irisin Protein\nRevealed by Single-Molecule Magnetic Tweezers

Irisin, a fibronectin III protein secreted by muscles\nduring physical\nexercise, plays a significant role in the browning of white fat and\ncell adhesion, highlighting the importance of its conformational transitions.\nIn this study, we investigated the folding and unfolding dynamics\nof a single irisin domain using a single-molecule manipulation technique\nknown as magnetic tweezers. In addition to the native state, irisin\ncan also fold transiently into a misfolded state. We determined the\nfolding free energies of the native and misfolded states as well as\ntheir force-dependent folding and unfolding rates. The free energy\nof the misfolded state is higher than that of the unfolded state,\nand the misfolded state has a homogeneous force-dependent unfolding\nrate. The stable native state demonstrates heterogeneous unfolding\nrates that are within ∼1 order of magnitude. Via comparison\nwith the well-studied 10th fibronectin III domain that has a partially\nfolded intermediate state, our study demonstrates that proteins with\nsimilar structure can have distinct folding pathways.