title: Selection Pressure in the Human Adenovirus Fiber Knob Drives Cell Specificity in Epidemic Keratoconjunctivitis.
abstract: Human adenoviruses (HAdVs) contain seven species (HAdV-A to -G), each associated with specific disease conditions. Among these, HAdV-D includes those viruses associated with epidemic keratoconjunctivitis (EKC), a severe ocular surface infection. The reasons for corneal tropism for some but not all HAdV-Ds are not known. The fiber protein is a major capsid protein; its C-terminal "knob" mediates binding with host cell receptors to facilitate subsequent viral entry. In a comprehensive phylogenetic analysis of HAdV-D capsid genes, fiber knob gene sequences of HAdV-D types associated with EKC formed a unique clade. By proteotyping analysis, EKC virus-associated fiber knobs were uniquely shared. Comparative structural modeling showed no distinct variations in fiber knobs of EKC types but did show variation among HAdV-Ds in a region overlapping with the known CD46 binding site in HAdV-B. We also found signature amino acid positions that distinguish EKC from non-EKC types, and by in vitro studies we showed that corneal epithelial cell tropism can be predicted by the presence of a lysine or alanine at residue 240. This same amino acid residue in EKC viruses shows evidence for positive selection, suggesting that evolutionary pressure enhances fitness in corneal infection, and may be a molecular determinant in EKC pathogenesis.
  
  
  OBJECTIVE
  Viruses adapt various survival strategies to gain entry into target host cells. Human adenovirus (HAdV) types are associated with distinct disease conditions, yet evidence for connections between genotype and cellular tropism is generally lacking. Here, we provide a structural and evolutionary basis for the association between specific genotypes within HAdV species D and epidemic keratoconjunctivitis, a severe ocular surface infection. We find that HAdV-D fiber genes of major EKC pathogens, specifically the fiber knob gene region, share a distinct phylogenetic clade. Deeper analysis of the fiber gene revealed that evolutionary pressure at crucial amino acid sites has a significant impact on its structural conformation, which is likely important in host cell binding and entry. Specific amino acids in hot spot residues provide a link to ocular cell tropism and possibly to corneal pathogenesis.
authors: Department of Ophthalmology, Howe Laboratory, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts, USA.
authors: Ashrafali M
authors: AM
authors: Ismail
authors: Department of Ophthalmology, Howe Laboratory, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts, USA.
authors: Ji Sun
authors: JS
authors: Lee
authors: Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA.
authors: David W
authors: DW
authors: Dyer
authors: Bioinformatics and Computational Biology Program, School of Systems Biology, George Mason University, Manassas, Virginia, USA.
authors: Donald
authors: D
authors: Seto
authors: Department of Ophthalmology, Howe Laboratory, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts, USA jaya_rajaiya@meei.harvard.edu james_chodosh@meei.harvard.edu.
authors: Jaya
authors: J
authors: Rajaiya
authors: Department of Ophthalmology, Howe Laboratory, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts, USA jaya_rajaiya@meei.harvard.edu james_chodosh@meei.harvard.edu.
authors: James
authors: J
authors: Chodosh
mesh_terms: D000072283:A549 Cells; D000258:Adenovirus Infections, Human / Q000821:virology*; D000260:Adenoviruses, Human / Q000235:genetics*; D000595:Amino Acid Sequence; D036022:Capsid Proteins / Q000235:genetics; D045744:Cell Line, Tumor; D003315:Cornea / Q000821:virology; D004279:DNA, Viral / Q000235:genetics; D005838:Genotype; D006801:Humans; D007637:Keratoconjunctivitis / Q000821:virology*; D010802:Phylogeny; D016415:Sequence Alignment / Q000379:methods; D017422:Sequence Analysis, DNA; D053586:Virus Internalization
chemical_list: D036022:Capsid Proteins; D004279:DNA, Viral