Avian H5: are humans an easy target?

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Avian H5 are humans an easy target?
Sinick Group Signe Christophersen and Nicholas
GauthierProtein Structure and Computational
Biology, Spring 2006
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Presentation Outline

• Introduction to H5
• Function
• Structure
• H5 Model
• Quality Validation
• H1/H5/H9 Comparisons
• Conclusions
• The Uncharacterized Protein
• Questions?

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Introduction H5 Function

• Target cell attachment
• Target receptors consist of sialic acid residues
  of glycosylated receptor proteins
• prefers binding a2-6 in humans
• prefers a2-3 linkage in avian
• Release of viral contents into the cell
• Lower pH in endosome causes change in HA that
  induces fusion of cell and virus membrane

Image taken from (then modified)
http//www.ch.ic.ac.uk/local/projects/sanderson/im
munology.htm
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Introduction H5 Structure 1

• Homotrimer of Heterodimers
• Synthesized in the cell as HA0
• Trimerizes and is transferred to cell surface

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Introduction H5 Structure 2

• Proteolytically cleaved to yield HA1 and HA2
  which are held together by disulfide bonds
• HA1 is shown in blue
• It contains the receptor binding site which is
  bound to an a2-3 (avian) linkage
• HA2 is shown in green
• 20 residues at the N-terminal are involved in
  cell/virus fusion

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Models of human H5

• Has avian H5 adapted to become human specific?
• Chose newest H5 isolated from human, DQ435202
• Create models using CPHmodels and HHPred
• Check quality of template
• Validate models
• Differences between H5 found in human and avian

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Quality of Template
1JSM was chosen as template for both
models Resolution 1.9Å R 0.234 Rfree 0.264

• PROCHECK ramachandran plot
• Most favoured regions 84.9
• Additionally allowed regions 14.2
• Generously allowed regions 0.5
• Disallowed regions 0,5

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Model Validation - ProQ
LG gt 2.5 very good model LG gt 4 extremely good
model MaxSub gt 0.1 fairly good model MaxSub gt
0.8 extremely good model
Template 1JSM CPH model
Template 1JSM HHPred model
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Model Validation VERIFY3d
HA1
HA2
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Receptor Binding Site
HHPred model CPH model Template, 1JSM
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Receptor Binding Site
Differences between H5 avian and H5 human isolate
193
221
186
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Receptor Binding Site
186 Av N Hu - S
193 Av K Hu - R
CPH model Template, 1JSM
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Human Adaptation How Can it Happen

• Avian H1 can become human specific E190D and
  G225D
• Avian H3 can become human specific Q226L and
  G228S
• Mutations introduced into H5 (A/Vietnam/1203/2004
  )

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Receptor Analogues
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Avian H5 Receptor binding
E190
Q226
G228
G225
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H1 vs. H5 Receptor Binding
Differences between H5 (1JSM) and H1 (1RVX)
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H1 vs. H5 Receptor Binding
H1 N193 H5 K193
H1 D225 H5 G225
H1 P186 H5 N186
H1, a2-6 receptor, H5, a2-3 receptor
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H9 from swine
a2-6 receptor a2-3 receptor
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H9 vs. H5 Receptor Binding
Differences between H5 (1JSM) and H9 (1JSD)
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H9 vs. H5 Receptor Binding
H9 V190 H5 E190
H9 L226 H5 Q226
H9 P186 H5 N186
H1, a2-6 H5, a2-3
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Conclusion

• H5 has not been adapted for humans
• Mutations rendering H5 a2-6 specific have not
  been identified
• We propose that human adaptation of H5 might
  happen via an H9 pathway, including the
  mutations E190V and Q226L. Also, the mutations
  N186P, L193N and G225D and might play a role.
• We suggest performing mutational analysis
  (including these mutations), followed by analyses
  of receptor binding properties to gain further
  information of a possible human adaptation of
  bird flu.

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Nonstructural Protein 1

• Structural model created from first 73 residues
• Structural model created using CPHmodels (shown
  at right)
• This domain is suggested to be a nucleic acid
  binding motif.
• Last 152 residues had no structural homolog

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Nonstructural Protein 1 (cont)

• Using the remaining 152 residues we
• Used HHpred to predict folds (see at right)
• ProtFun predicted to be an enzyme (65),
  involvement in amino acid biosynthesis (28)
• SignalP no signal peptide, and is non-secretory
• TMHMM found no transmembrane regions

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Questions?
Sinick Group Signe Christophersen and Nicholas
GauthierProtein Structure and Computational
Biology, Spring 2006