Mechanochemical Evolution of the Giant Muscle Protein Titin as Inferred from Resurrected Proteins
The sarcomere-based structure of muscles is conserved among vertebrates; however, vertebrates muscle physiology is extremely diverse. A molecular-level explanation for this muscle diversity and its evolution has not yet been proposed. In our group, we use phylogenetic analysis and single-molecule atomic force spectroscopy (AFS) to investigate the nanomechanical evolution of titin, a giant protein responsible for the elasticity, integrity and signal transduction of muscle filaments.Here, I will present how we bring back to life eight-domain fragments of titin from different extinct species ranging from 179 to 356 million years ago (Mya), and compare them with their modern descendants. Using AFS we observe that the mechanical stability of titin domains and the presence of disulfide bonds are key elements in the evolution of titin. Our experiments demonstrate that ancient titin molecules were rich in disulfide bonds and displayed high mechanical stability. These mechanochemical elements seem to have changed over the course of evolution creating a paleomechanical trend that correlates with animal physiological properties such as heart rate and body size. We hypothesize that mechanical adjustments in titin contributed to physiological changes that allowed the muscular development and morphological diversity of modern vertebrates. While small animals seem to have stiffer domains with more disulfide bonds, large animals show weaker domains with fewer disulfides. A comparative analysis between animal physiological properties and titin mechanical properties allows us estimating the heart rate and body size of the ancestors of modern tetrapods, including sauropsids and mammals.