A Conserved Structural Core in Myosin and Kinesin Motors Revealed by Non-Homologous Superimposition

The molecular motors myosin and kinesin are classic examples of convergent evolution, performing motile functions on different cytoskeletal tracks with minimal sequence homology. While their shared structural fold has been noted, the true extent of their geometric identity has remained elusive. Here, we present computational evidence of a deeply conserved, two-part structural core common to both motor families. Through a targeted, non-homologous superposition, we identified a four-residue constellation within their motor domains (PDB: 1fmv, 3kin) exhibiting a near-perfect geometric identity (RMSD = 0.096 Å). Crucially, this identity is achieved via a rigidly aligned core (a β-strand in both proteins) and a flexible bridge, which connects the core via disparate secondary structures (a loop in Kinesin vs. a β-strand in Myosin). This finding challenges the conventional understanding of convergent evolution, suggesting a common, ancient origin based on an immutable geometric principle. This "core-bridge" mechanism represents a fundamental blueprint for molecular motor function.