Research ArticleVIROLOGY

Human adenovirus type 26 uses sialic acid–bearing glycans as a primary cell entry receptor

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Science Advances  04 Sep 2019:
Vol. 5, no. 9, eaax3567
DOI: 10.1126/sciadv.aax3567
  • Fig. 1 HAdV-D26K forms a local basic area in the apical depression to facilitate sialic acid binding despite an overall acidic predicted isoelectric point.

    (A) HAdV-D26K has low (56.76%) sequence identity with fiber knobs known to bind sialic acid by a similar mechanism and an acidic isoelectric point. The electrostatic potential surfaces of HAdV-D8K (B), HAdV-D64/37 (C), and HAdV-D19p (D) fiber knobs are highly basic, especially about the central depression about the threefold axis. (E) HAdV-D26 fiber knob is less basic overall but maintains positive potential in the central depression. Surfaces are displayed at ±10 mV, and the two residues that differ between HAdV-D19p and HAdV-D37/64 are shown as green sticks.

  • Fig. 2 HAdV-D26K shares key binding residues with sialic acid–using adenoviruses and exploits sialic acid to infect cells.

    (A) Sequence alignment of HAdV-D26K shows conservation of key binding residues with known sialic acid–binding adenoviruses; top numbering is according to HAdV-D26K. Residues boxed in red form polar contacts with sialic acid, those boxed in black denote contact sialic acid via water bridge, and those boxed in orange indicate hydrophobic contacts; all HAdV-D26K polar contacts also form water bridges. Neuraminidase treatment does not reduce the ability of HAdV-D5/B35K (B) or HAdV-C5 (C) to infect SKOV-3 (ovarian adenocarcinoma), BT-20 (breast carcinoma), or MDA-231 (metastatic breast adenocarcinoma) cells, while HAdV-D5/D26K (D) is significantly inhibited. n = 3 biological replicates; error bars indicate ±SD.

  • Fig. 3 Sialic acid binds in the apical depression of HAdV-D26 fiber knob protein.

    The map shows clear density for a ligand (A), which is best described by a double conformer of sialic acid (B). (C) Sialic acid (orange) is seen to bind in three locations in the apical depression of the HAdV-D26 fiber knob, bridging between monomers (shades of blue) of the trimeric assembly. Crystallization statistics are provided in table S1; 2FoFc map (blue mesh, σ = 1.5) and FoFc (green mesh, σ = 3.0).

  • Fig. 4 HAdV-D26K forms a complex interaction network of hydrophobic and electrostatic interactions with sialic acid.

    Sialic acid (orange) is seen to bind HAdV-D26 (A) and HAdV-D37 (B) through a network of polar contacts (red dashes) and hydrogen bonds (blue dashes). The interaction is stabilized by hydrophobic interactions (red regions on white surface) with the N-acetyl CH3 group, but different residues in HAdV-D26 (C) and HAdV-D37 (D). Waters are shown as cyan spheres, residues forming comparable contacts in HAdV-D26 and HAdV-D37 are shown as blue sticks, and other residues are shown as green sticks. Oxygen and nitrogen are seen in red and blue, respectively.

  • Fig. 5 HAdV-D26K uses an induced-fit mechanism in sialic acid binding.

    HAdV-D26K residue Gln348 can occupy multiple conformations, with a greater preference for conformation A (capable of forming a polar contact with the glycerol arm of sialic acid) at pH 8.0 (A) than at pH 4.0 (B). (C) Ile324 has two conformations when HAdV-D26K is unliganded (PDB 6FJO). (D) However, upon sialic acid binding, the Ile324 adopts a single confirmation, creating a hydrophobic indentation around the N-acetyl methyl group bounded by Ile324, Ile310, and the ring of Tyr312.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/9/eaax3567/DC1

    Fig. S1. Sialic acid forms a stable interaction with HAdV-D26K 654 at both pH 4.0 (PDB 6QU6) and pH 8.0 (PDB 6QU8).

    Fig. S2. Structure of sialic acid (Neu5Ac) in a biologically relevant conformation.

    Fig. S3. HAdV-D26K forms a similar interaction with sialic acid at both pH 4.0 (PDB 6QU6) and pH 8.0 (PDB 6QU8) through a combination of polar, water bridge, and hydrophobic interactions.

    Fig. S4. Species D adenoviruses conserve known sialic acid–binding residues.

    Table S1. Data collection and refinement statistics for structures generated in this study.

    Table S2. Primers used to generate recombineering PCR products in this study.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Sialic acid forms a stable interaction with HAdV-D26K 654 at both pH 4.0 (PDB 6QU6) and pH 8.0 (PDB 6QU8).
    • Fig. S2. Structure of sialic acid (Neu5Ac) in a biologically relevant conformation.
    • Fig. S3. HAdV-D26K forms a similar interaction with sialic acid at both pH 4.0 (PDB 6QU6) and pH 8.0 (PDB 6QU8) through a combination of polar, water bridge, and hydrophobic interactions.
    • Fig. S4. Species D adenoviruses conserve known sialic acid–binding residues.
    • Table S1. Data collection and refinement statistics for structures generated in this study.
    • Table S2. Primers used to generate recombineering PCR products in this study.

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