Figure 3.

Mapping of compensatory mutation segments onto the 3D structure of the spike (S) protein protomer with the RBD-up form. (A) Different domains and subdomains belonging to S1 (upper part) and S2 (lower or base part) units of the S-protomer. (B) Mapped structural segments C1, C2, and C3 on the N-terminal domain (NTD) (pink) involving differently composed β strands. (C) Schematic presentation of the functional significance of C1, C2, and C3 that differentially establishes a long-range allosteric communication with the RBD (blue) mutation site, where C1, C2, and C3 residues act as allosteric activators capable of propagating the mutation-induced allosteric signals to a distant allosteric site in RBD through a combination of structural changes and modulations of dynamics.