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. Author manuscript; available in PMC: 2019 Oct 1.
Published in final edited form as: Trends Microbiol. 2018 Apr 19;26(10):841–853. doi: 10.1016/j.tim.2018.03.005

Figure 3. Prefusion structure of the HA protein and residues known to affect its stability.

Figure 3

(A) HA domain structure. HA1 domains include the fusion (F1, blue), vestigial esterase (VE, yellow), and receptor-binding domain (RBD, green). HA2 includes a stalk domain (orange), transmembrane region (TM, white), and cytoplasmic tail (CT, white). Solid circles identify residues to which stabilizing or destabilizing mutations have been identified in review articles [21, 22] and primary manuscripts [54, 60–62, 66, 70, 74–87]. (B) Domain insertion in the HA protein, adapted from [116]. (C) Prefusion structure of one HA monomer. (D) Prefusion structure of an HA trimer. Residues regulating stability (black balls) are located throughout the trimer in the receptor-binding pocket (R.B.P.), between HA1 heads (head-head), between the HA1 head the stalk (head-stalk), in the B loop and adjacent helix C (B loop area), in the core of the coiled coil (core), in the HA1 stalk, between helix A and the coiled coil (helix A), in and around the fusion peptide pocket (fus. pep. & pocket), and in the membrane-proximal region (M.P.R.). In panel D, two protomers are colored gray. Structures were generated using MacPYMOL using A/California/4/2009 (H1N1) protein data bank structure 3UBE [117].