The SII-P was discovered by Ostrem et al. in 2013. The team reported the first set of covalent KRAS G12C binders that were occupying this pocket. In total, 12 KRAS(G12C)-inhibitor cocrystal structures were released, including disulphide-, vinyl sulphonamide-, and acrylamidebased covalent inhibitors (Table ). Most of these early inhibitors (8 of 12), appear in a distinct switch-II configuration, where switch-II resides in a more open conformation, and the conserved water site is distorted (Table , Figure ). Notably, in five of these crystal structures, the ligand is found to occupy the pocket only in one of the monomers (while three KRAS proteins are forming the asymmetric unit) (Table ). In addition, in one of these structures the switch-II is disordered (PDB ID: 4M21) (Figure ). Therefore, due to their distinct configuration, we excluded these eight structures from our WaterMap analysis. The other four structures all display the Thr58 associated conserved water in their structures (Table ). WaterMap simulations suggest that two of the structures (PDB IDs: 4LUC; 4LV6) appear with neighboring adjacent hydration site(s) (Figure , Figure ), while the other two (PDB IDs: 4LYH; 4M22) 32 exhibit an isolated conserved water (Figure ). The estimated energies of the conserved water are higher with the structures of isolated hydration sites (WaterMap DG: +9.68 and +11.37 kcal/mol for isolated hydration sites; +4.78 and +7.17 kcal/mol for conserved hydration site with adjacent hydration sites). The first reported selective KRAS(G12C) inhibitor with notable cellular efficacy was ARS-853 . Interestingly, WaterMap predicts the lowest energy (DG: +5.09 kcal/mol) for this hydration site from all the isolated hydration sites with all the publicly available KRAS SII-P cocrystallized complexes (Figure ). This is due to fact, that piperazine of the ARS-853 is optimally placed to offer the protonated nitrogen towards the water, resulting in low enthalpy of the conserved hydration site (DH: -0.18 kcal/mol). Nevertheless, the entropy of the hydration site is still estimated as high, resulting in total of a high energy hydration site (DG: +5.09 kcal/mol). Indeed, if the Thr58 associated conserved water is present in the structure, the more recent KRAS(G12C) SII-P binders reported after ARS-853 tend to contain only an isolated conserved high-energy water (total of 32 published co-crystal structures). The only exceptions are where the conserved water appears with adjacent hydration sites, such as the lower affinity fragment GNE-2897 reported by Genentech (PDB ID: 7MDP) , co-crystallized together with an antibody, as well as Boehringer-Ingelheim's fragment "compound 12" and BI-0474 (PDB IDs: 8AFC, 8AFB) (Table ; Figure ). In addition to this, BI-0474 structure (PDB ID: 8AFB) 50 also displays two conformations of Lys16 (normal and shifted) with a probability of 0.5 for both, which in turn has an impact on the WaterMap predicted hydration site pattern (Table ; Figure ). The WaterMap suggests that all these several distinct compounds with the isolated hydration site exhibit truly a high-energy hydration site in this location (DG: >8.50 kcal/mol).