In the initial Inactive Val51 model, the Val51 φ dihedral matches that of the optimized Inactive-ES structure (-138°) by construction. During geometry optimizations, the dihedral adjusts to -111° in Inactive Val51. This adjustment is consistent with the description of a third oxyanion strand conformation identified in MD simulations as an intermediate conformation of the Val51 dihedral flip. The partial dihedral rotation introduces a weak interaction (less than 0.5 kcal/mol) between the Gln Oε lone pair electrons and the π* orbital of backbone Gly50 C=O. This type of n-π* interaction to stabilize an oxyanion tetrahedral intermediate has precedence in aspartic proteases and, therefore, could be a catalytically relevant state in IGPS. Although Gly52 does not contribute to oxyanion stabilization in the inactive conformation, as previously suggested, repositioning of the oxyanion strand enables such stabilizing interactions, as shown in the Inactive Val51 model. In addition, the new crystallographic conformation of IGPS (7ac8 chains E/F) also results in a catalytically competent oxyanion hole geometry involving Val51. From the energetic perspective both the Active and Inactive Val51 models are consistent with experimental kinetic data.