Poster abstracts
Poster number 12 submitted by Narayanan Puthillathu
Dynamics of K-Ras G12D Inhibition
Narayanan Puthillathu (Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, OH, USA), Alexander L Hansen (Campus Chemical Instrument Center, The Ohio State University, Columbus, OH, USA), Lei Bruschweiler-Li (Campus Chemical Instrument Center, The Ohio State University, Columbus, OH, USA), Rafael Bruschweiler (Department of Chemistry & Biochemistry, The Ohio State University, Columbus, OH, USA)
Abstract:
K-Ras is an oncogenic signaling protein involved in 22.5% of human cancers. The K-Ras-G12D mutation is the most frequent mutation causing pancreatic cancer. Currently, no drugs targeting G12D mutation are clinically approved to treat this cancer. K-Ras acts as a switch for kinase signaling by exchanging between the GTP-bound (active) vs. GDP-bound (inactive) forms. The small molecule ligand MRTX1133 has demonstrated in vitro efficacy in binding and inhibiting G12D mutants and is expected to progress to clinical trials for treating pancreatic adenocell carcinoma. Here, we present the atomistic mechanisms of G12D inhibition by MRTX1133 using nuclear magnetic resonance (NMR) based relaxation dispersion techniques, including the Carr-Purcell-Meiboom-Gill spin echo pulse train (CPMG) and chemical exchange saturation transfer (CEST) experiments. MRTX1133 binds to the Switch II pocket cleft and allosterically inhibits K-Ras. Crystal structures indicate that the P-loop and Switch II are predominantly involved in drug contact, with 37 residues residing within a 5 Angstrom distance of the drug. The binding effectively inhibits GTP hydrolysis of the K-Ras-G12D-GTP form. It directly binds the G60 residue in the active site proposed to be involved in the GTP hydrolysis mechanism. MRTX1133 quenches the millisecond dynamics of the Switch-II region of the K-Ras-G12D mutant. The chemical shift perturbation of the K-Ras-G12D-drug complex converges to the same ground-state structure for both GTP and GDP-bound forms. A possible MRTX1133 mechanism of inhibition via allosteric rigidification of switch regions will be discussed.
Keywords: K-Ras, Protein dynamics, NMR