The 1.1 Å x-ray crystal structure of oncogenic KRAS G13D, reported by Hunter and colleagues (p.1325), reveals a destabilizing interaction between the aspartate side-chain and GDP. The calculated electrostatic potential surface map highlights the negative charge (red) introduced by the aspartate, which disrupts the normally positively charged (blue) nucleotide binding pocket and repels adjacent negatively charged phosphates in GDP, explaining the enhanced rate of nucleotide exchange observed for this mutant.