194 To corroborate these findings, we also evaluated the susceptibility of both BA.2.86 pseudoviruses
195 to neutralization by the dimeric human-ACE2-Fc protein, in comparison to BA.2, XBB.1.5, and
196 EG.5.1. In agreement with the SPR data, both versions of BA.2.86 were >2-fold more sensitive
197 to ACE2 inhibition than XBB.1.5 and EG.5.1, as determined by their IC50 values (Figure 4b). A
198 potential explanation for this heightened affinity may reside in the intrinsic charge properties of
199 the two interacting molecules. The region of human ACE2 targeted by the RBD is negatively
charged, while the Omicron RBD itself is positively charged32 200 . The higher receptor binding
201 affinity of the BA.2.86 spike might be attributed to the additional positive charges associated with
202 mutations V445H, N460K, N481K and A484K (Figure 4c). Only the N460K mutation is shared
203 with the spikes from XBB.1.5 and EG.5.1.