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Detailed Structure of the H2PO4––Guanosine Diphosphate Intermediate in Ras-GAP Decoded from FTIR Experiments by Biomolecular Simulations

Xia, Fei, Rudack, Till, Cui, Qiang, Kötting, Carsten, Gerwert, Klaus
Journal of the American Chemical Society 2012 v.134 no.49 pp. 20041-20044
Fourier transform infrared spectroscopy, GTPase-activating proteins, X-radiation, biochemical pathways, energy conversion, guanosine diphosphate, hydrogen, ligands, signal transduction
Essential biochemical processes such as signal transduction, energy conversion, or substrate conversion depend on transient ligand binding. Thus, identifying the detailed structure and transient positioning of small ligands, and their stabilization by the surrounding protein, is of great importance. In this study, by decoding information from Fourier transform infrared (FTIR) spectra with biomolecular simulation methods, we identify the precise position and hydrogen network of a small compound, the guanosine diphosphate (GDP)–H₂PO₄– intermediate, in the surrounding protein–protein complex of Ras and its GTPase-activating protein, a central molecular switch in cellular signal transduction. We validate the simulated structure by comparing the calculated fingerprint vibrational modes of H₂PO₄– with those obtained from FTIR experiments. The new structural information, below the resolution of X-ray structural analysis, gives detailed insight into the catalytic mechanism.