Figure 1.

Comparison of the HKU4-RBD, HKU5-RBD, MERS-RBD, and SARS-RBD Sequences

(A) Phylogenetic tree generated using MEGA (Tamura et al., 2013) with the indicated RBD sequences.

(B) Structure-based sequence alignment. The secondary structure elements are defined based on an ESPript (Gouet et al., 1999) algorithm and are labeled as in a previous report on the MERS-RBD structure (Lu et al., 2013). Spiral lines indicate α or 3₁₀ helices, while arrows represent β strands. Helices α1 and η4 and strands β2 and β11 are not preserved in the HKU4-RBD structure and are marked in red. The element equivalent to the MERS-RBD helix α3 exhibits characteristics of a 3₁₀ helix in HKU4-RBD and is therefore labeled as η′. The external subdomain is highlighted by enclosure with a red box. The two deletions in HKU5-RBD are marked with blue lines. The Arabic numerals 1–4 indicate cysteine residues that pair to form disulfide bonds. See also Figure S3.