Protein intrinsic disorder and influenza virulence: the 1918 H1N1 and H5N1 viruses

Abstract

Background: The 1918 H1N1 virus was a highly virulent strain that killed 20-50 million people. The cause of its virulence remains poorly understood.

Methods: Intrinsic disorder predictor PONDR VLXT was used to compare various influenza subtypes and strains. Three-dimensional models using data from X-ray crystallographic studies annotated with disorder prediction were used to characterize the proteins.

Results: The protein of interest is hemagglutin (HA), which is a surface glycoprotein that plays a vital role in viral entry. Distinct differences between HA proteins of the virulent and non-virulent strains are seen, especially in the region near residues 68-79 of the HA2. This region represents the tip of the stalk that is in contact with the receptor chain, HA1, and therefore likely to provide the greatest effect on the motions of the exposed portion of HA. Comparison of this region between virulent strains (1918 H1N1 and H5N1) and less virulent ones (H3N2 and 1930 H1N1) reveals that predicted disorder can be seen at this region among the more virulent strains and subtypes but is remarkably absent among the distinctly less virulent ones.

Conclusion: The motions created by disorder at crucial regions are likely to impair recognition by immunological molecules and increase the virulence of both the H5N1 and the 1918 H1N1 viruses. The results help explain many puzzling features of the H5N1 and the 1918 H1N1 viruses. Summarizing, HA (and especially its intrinsically disordered regions) can serve as a predictor of the influenza A virulence, even though there may be other proteins that contribute to or exacerbate the virulence.

Figure 1

Three-dimensional representation of the HA with predicted disorder annotation. The regions in red represent areas predicted to be disordered by VLXT. Conversely, the blue areas represent regions predicted to be ordered. A) 1918 H1N1 HA₂, 1ruz.pdb B)1930 H1N1 1ruy.pdb, C) 1934 H1N1, 1rvx.pdb D) H5N1, 2fk0.pdb E) H5N1, 2ibx.pdb F) H5N1, 1jsn.pdb G) H9N2.pdb, Swine H) H3N2, "Hong Kong Flu-1968 " Progenitor, Sample from 1963 I) H7N3, Avian.

Figure 2

PONDR^@ VLXT and B-factor plots of the HA₂. The blue curves represent the VLXT score, while the black ones represent the normalized B-factor. A) 1918 H1N1 HA2, 1ruz.pdb B)1930 H1N1 1ruy.pdb, C) 1934 H1N1, 1rvx.pdb D) H5N1, 2fk0.pdb E) H5N1, 2ibx.pdb F) H5N1, 1jsn.pdb G) H9N2, 1jsd.pdb, Swine H) H3N2, "Hong Kong Flu-1968 " Progenitor, Sample from 1963, 1mqn.pdb I) H7N3, Avian, H7N3, Italy, Avian, 1it8 [24,22,20].

Figure 3

Protein sequence of HA₂ around tesidue 68. Vertical lines show where mutations have taken place. The numbers denote the residue numbers.