Fig. 4: Comparison of the sialic acid-binding site in the apo and closed holo S1^A domains.

a,b, The S1^A sialic acid-binding pocket in the apo (a) and holo (b) states. The e1 loop (yellow), e2 loop (green) and pockets p1 and p2 are indicated. The disialoside (‘ligand’) is shown in pink; GlcNAc residues of the N29 N-linked glycan are shown in green. Note the conformational differences in the e1 loop in the holo as compared to the apo state. c,d, Side-by-side comparison of the S1^A domain in the apo (c) and closed holo state (d). The hinge segments connecting subdomains S1^A1 and S1^A2 are highlighted with the e1 loop in yellow. Dashed lines indicate the angle between the subdomains.