Fig. 9.

Proposed trimer structure model of the PIV5 TMD. (a) Top view of the trimer structure, showing L493F, L500F, and L504F interhelical ¹⁹F–¹⁹F distances. These agree with the experimentally measured ¹⁹F–¹⁹F distances. (b) Helical wheel diagram for the trimeric TMD, with L493F and L504F at the d position of the heptad repeat, forming close interhelical contacts, while L500F lies at the g position, giving longer interhelical distances. (c) Side views of the trimer structure, showing the locations of ¹³C, ¹⁵N-labeled residues in the two mixed labeled samples (Table 1). Representative interhelical distances between S505 and V506, and between G494 and L495, are much longer than can be measured using ¹³C spin diffusion NMR. This is further illustrated in the helical wheel diagram for the S505–V506 pair.