Understanding protein packing and morphological transformations in virus shells (capsids) during their maturation can be pivotal for developing new antiviral strategies. Anže Božič and coworkers studied how these principles manifest themselves in icosahedral viral capsids assembled from identical symmetric structural units (capsomeres). To rationalize such shells, they modeled capsomers as symmetrical groups of identical particles interacting with a short-range potential, typical of the classic Tammes problem. The capsomere particles are assumed to retain their relative positions on the vertices of planar polygons placed on the spherical shell and to interact only with the particles from other capsomeres. Minimizing the interaction energy enforces equal distances between the nearest particles belonging to neighboring capsomeres and minimizes the number of different local environments. Thus, the model implements the Caspar and Klug quasi-equivalence principle, leading to packings strikingly similar to real capsids. They then studied the reconstruction of protein trimers into dimers in a Flavivirus shell during its maturation, connecting the relevant structural changes with the modifications of the electrostatic charges of proteins wrought by the oxidative switch in the bathing solution that is essential for the process. They highlight the key role of pr peptides in the shell reconstruction and show that the highly ordered arrangement of these subunits in the dimeric state is energetically favored at a low pH level. They also discuss the electrostatic mechanisms controlling the release of pr peptides in the last irreversible step of the maturation process.

Published in:
Rochal et al., Nanoscale Adv., 2022,4, 4677-4688