Dynamic Interplay\nof Loop Motions Governs the Molecular\nLevel Regulatory Dynamics in Spleen Tyrosine Kinase: Insights from\nMolecular Dynamics Simulations

The spleen tyrosine kinase (Syk) is a key regulator in\nimmune cell\nsignaling and is linked to various mechanisms in cancer and neurodegenerative\ndiseases. Although most computational research on Syk focuses on novel\ndrug design, the molecular-level regulatory dynamics remain unexplored.\nIn this study, we utilized 5 × 1 μs all-atom molecular\ndynamics simulations of the Syk kinase domain, examining it in combinations\nof activation segment phosphorylated/unphosphorylated (at Tyr525,\nTyr526) and the “DFG”-Asp protonated/deprotonated (at\nAsp512) states to investigate conformational variations and regulatory\ndynamics of various loops and motifs within the kinase domain. Our\nfindings revealed that the formation and disruption of several electrostatic\ninteractions among residues within and near the activation segment\nlikely influenced its dynamics. The protein structure network analysis\nindicated that the N-terminal and C-terminal anchors were stabilized\nby connections with the nearby stable helical regions. The P-loop\nshowed conformational variation characterized by movements toward\nand away from the conserved “HRD”-motif. Additionally,\nthere was a significant correlation between the movement of the β3-αC\nloop and the P-loop, which controls the dimensions of the adenine-binding\ncavity of the C-spine region. Overall, understanding these significant\nmotions of the Syk kinase domain enhances our knowledge of its functional\nregulatory mechanism and can guide future research.