Three-dimensional structure of the neuraminidase of influenza virus A/Tokyo/3/67 at 2.2 A resolution

An atomic model of the tetrameric surface glycoprotein neuraminidase of influenza virus A/Tokyo/3/67 has been built and refined based on X-ray diffraction data at 2.2 A resolution. The crystallographic residual is 0.21 for data between 6 and 2.2 A resolution and the r.m.s. deviations from ideal geometry are 0.02 A for bond lengths and 3.9 degrees for bond angles. The model includes amino acid residues 83 to 469, four oligosaccharide structures N-linked at asparagine residues 86, 146, 200 and 234, a single putative Ca2+ ion site, and 85 water molecules. One of the oligosaccharides participates in a novel crystal contact. The folding pattern is a beta-sheet propeller as described earlier and details of the intramolecular interactions between the six beta-sheets are presented. Strain-invariant residues are clustered around the propeller axis on the upper surface of the molecule where they line the wall of a cavity into which sialic has been observed to bind. Strain-variable residues implicated in binding to antibodies surround this site.     

Epidemiological studies on echovirus type 18 infection in Toyama Prefecture

Echovirus type 18 (echo 18) was isolated from six aseptic meningitis children in Fukumitsu-machi, Toyama Prefecture, from July to August, 1980. This was the first virologically-confirmed epidemic of aseptic meningitis due to echo 18 in Japan. Epidemiological studies on the prevalence of this virus among the inhabitants in Toyama Prefecture were also performed. The results are summarized as follows. (1) Significant increases in neutralizing antibody titers against echo 18 were observed in all the paired sera of aseptic meningitis patients from whom echo 18 was isolated. (2) In October, 1980, echo 18 was also isolated from healthy children or from infants suffering from gastroenteritis in other areas of Toyama Prefecture. (3) Among the sera collected from 50 children (aged smaller than or equal to 12) in Fukumitsumachi in December, 1980, neutralizing antibodies against echo 18 were detected only in the younger groups (aged smaller than or equal to 8), 58.9% of these age groups showing a titer of 4 or higher. (4) Another epidemic around 1963 by echo 18 in Toyama Prefecture was retrospectively suggested by the examinations of sera collected in 1978 and 1981 from inhabitants in various areas of Toyama Prefecture. (5) Neutralizing antibody titers against the strain isolated, No. 35'80, were significantly higher than those against strain 'Metcalf,' the prototype of echo 18, in most sera including both aseptic meningitis patients and healthy inhabitants.     

Structure of an escape mutant of glycoprotein N2 neuraminidase of influenza virus A/Tokyo/3/67 at 3 A

The three-dimensional structure of the membrane glycoprotein neuraminidase of an escape mutant of the influenza virus strain A/Tokyo/3/67 has been determined to 3 A (1 A = 0.1 nm) resolution by X-ray diffraction. The mutant virus, selected by growing the virus in the presence of a monoclonal antibody to the neuraminidase, is shown to have undergone a single amino acid change of lysine to glutamic acid at residue 368. The three-dimensional structure of the neuraminidase is identical with that reported for A/Tokyo/3/67, except for a purely local adjustment of the structure at position 368.     

Avian-to-human transmission of the PB1 gene of influenza A viruses in the 1957 and 1968 pandemics.

We determined the origin and evolutionary pathways of the PB1 genes of influenza A viruses responsible for the 1957 and 1968 human pandemics and obtained information on the variable or conserved region of the PB1 protein. The evolutionary tree constructed from nucleotide sequences suggested the following: (i) the PB1 gene of the 1957 human pandemic strain, A/Singapore/1/57 (H2N2), was probably introduced from avian species and was maintained in humans until 1968; (ii) in the 1968 pandemic strain, A/NT/60/68 (H3N2), the PB1 gene was not derived from the previously circulating virus in humans but probably from another avian virus; and (iii) a current human H3N2 virus inherited the PB1 gene from an A/NT/60/68-like virus. Nucleotide sequence analysis also showed that the avian PB1 gene was introduced into pigs. Hence, transmission of the PB1 gene from avian to mammalian species is a relatively frequent event. Comparative analysis of deduced amino acid sequences disclosed highly conserved regions in PB1 proteins, which may be key structures required for PB1 activities.