Figure 5

The Complex Structure of HKU4-RBD Bound to hCD26

(A) The overall structure. The two 1:1 complexes related by a two-fold axis (vertical arrow) are shown in cartoon and surface representations, respectively. The core and external subdomains of HKU4-RBD and the β-propeller and hydrolase domains of hCD26 are individually labeled and highlighted in orange, cyan, magenta, and green, respectively. The propeller blades (I–VIII) and the protein N/C termini are marked.

(B) A magnified view of the HKU4-RBD structure and the ligand/receptor interface. The secondary structure elements are specified by ESPript and labeled for the viral ligand. Yellow sticks marked with Arabic numbers indicate disulfide bonds. For the receptor, only propeller blades IV and V that engage HKU4-RBD are shown, using a surface representation.

(C–E) The important contact sites are marked with boxed letters A–E and are further delineated for interaction details as follows. (C) A solid network of H bond and salt bridge interactions. (D) A small patch of hydrophobic interactions. (E) Extra H bond contacts contributed by a carbohydrate moiety linked to hCD26 N229. The residues involved and the carbohydrates referred to are shown and labeled. See also Tables S1 and S2.