view article
Figure 7
Flexibility of dynamic loops. (a) Tapasin loop E11–K20 modeled from various complexes is superimposed on the α1 helix. MHC-I is blue and the tapasin of each complex is color-coded according to the legend in the panel [PDB entries 3f8u (6), 7tue (4) and 6eny (3) are missing a number of residues on the loop]. The conformation of the loop varies indicating the mobility and flexibility of this loop. The α2–1 helices are drawn towards tapasin in various degrees indicating the openness of peptide groove in different structures. (b) Tapasin loop Q189–H195, the complexes are superimposed on α2–1. The loop interacts with β7 and β8 underneath the peptide-binding groove. Inset: tapasin loop from PDB entries 7tuf and 3f8u, the loop occupies a higher position. When tapasin is complexed with MHC-I (e.g. PDB entries 7qng, 7qpd, 7tue and 6eny), the loop is pushed down by 5–10 Å. (c) Tapasin loop P69–S110 (color) and TAPBPR loop C101–Q126 (gray). Tapasin has a much longer loop P69–S110 (40 aa) than that of TAPBPR (26 aa) which increased the interaction between the β8 loop and S82–K84 of tapasin.

IUCrJ
Volume 11| Part 3| May 2024| Pages 287-298
ISSN: 2052-2525
https://doi.org/10.1107/S2052252524002768