Fig. 6.

D1-E22-D23-K28 cluster in populations A and B. (a) Top view of the D1-E22-D23-K28 cluster in population A (left) and population B (right). In population A, charged residue pairs are brought into close proximity by the N-terminal fold, resulting in electrostatic interactions that stabilize and tether the N-terminus in position. Contrary to population A, the linear conformation of the inner layers in population B does not allow many electrostatic interactions. However, the D23–K28 salt bridge remains and is now able to be fully involved. (b) Ribbon view of population A highlights the out-of-plane displacement of a monomer in red up to 10 Å. (c) (left) Cartoon representation of population A with three individual monomers highlighting interactions between monomers (n), (n + 1), and (n + 2). Residues of interest are highlighted (colors represent different monomers). The N-terminus of monomer (n) (green) is displaced above the monomer plane and interacts with K28 two monomers above (n + 2). Similarly, D23 interacts with K28 on the monomer (n + 1). (right) In contrast, the same residues of the electrostatic cluster are interacting in an intermolecular fashion in population B, leading to the absence of stagger and inter-molecular stabilizing interactions.