Disease relevance of NB

• RNA segment 6 of the influenza B virus genome codes for a previously unidentified polypeptide designated NB [1].
• A protein analogous to NB has not been found with influenza A virus, and this represents a major difference between the two virus types [1].
• NB has not been found in virions [1].

High impact information on NB

• Sucrose gradient sedimentation and analysis of the structure of the mRNA by nuclease S1 mapping and sequence analysis by the primer extension method indicated that polypeptide NB and the neuraminidase are translated from a single bicistronic mRNA [1].
• The amino acid sequence of polypeptide NB deduced from the nucleotide sequence of the B/Lee/40 strain consists of 100 amino acids with a molecular weight of 11,242 [1].
• Polylactosaminoglycan modification of a small integral membrane glycoprotein, influenza B virus NB [2].
• Expression of mutants of NB lacking either one or both of the normal N-terminal sites of asparagine-linked glycosylation indicated that both carbohydrate chains are modified to contain polylactosaminoglycan [2].
• Treatment of infected-cell surfaces with proteinase K and endoglycosidase F and immunoprecipitation with a site-specific antibody suggests that the 18-amino-acid NH2-terminal region of NB is exposed at the cell surface [3].

Biological context of NB

• The mRNA derived from influenza B virus RNA segment 6 is functionally bicistronic and encodes the NB and NA glycoproteins in different, overlapping reading frames [4].
• The nucleotide sequence context of the first AUG codon conforms closely with the established 5'-CC(A/G)CCAUGG-3' consensus sequence (M. Kozak, Nucleic Acids Res. 15:8125-8148, 1987), which should favor initiation of NB protein synthesis at this site, yet NB and NA are found to accumulate in approximately equal amounts in infected cells [4].
• NB is short auxiliary protein with ca. 100 amino acids, encoded in the viral genome of influenza B [5].
• The NB protein of influenza B virus is not necessary for virus replication in vitro [6].
• An amino-acid substitution in the influenza-B NB protein affects ion-channel gating [7].

Anatomical context of NB

• Its glycosylation and orientation in the membrane were shown to be equivalent to that of NB in the plasma membrane of virus-infected cells [8].
• However, a much lesser hyperpolarization (approximately -130 mV) was able to evoke a similar current from oocytes that expressed the cellular proteins IsK and phospholemman, the synthetic protein SYN-C, and the NB protein of influenza B virus [9].

Associations of NB with chemical compounds

• Studies on the synthesis of the influenza V virus NB glycoprotein [10].
• Unglycosylated NB, expressed either in influenza B virus-infected cells treated with tunicamycin or in cells expressing the NB mutant lacking both N-linked glycosylation sites, was expressed at the cell surface, indicating that NB does not require carbohydrate addition for transport [2].
• Amantadine blocks channel activity of the transmembrane segment of the NB protein from influenza B [5].

Analytical, diagnostic and therapeutic context of NB

• Immunoprecipitation of viral proteins from infected cells using hyperimmune mouse serum has demonstrated antigenic cross-reactivity among the NB proteins of the four virus strains studied [10].
• Oligonucleotide-directed mutagenesis to eliminate each of the four potential sites of N-linked glycosylation and expression of the mutant NB proteins in eucaryotic cells suggest that the two sites adjacent to the NH2 terminus are glycosylated [3].
• Selection of this carbohydrate-containing form of NB with Datura stramonium lectin, its susceptibility to digestion by endo-beta-galactosidase, and determination of the size of NBp glycopeptides by gel filtration chromatography suggested that the increase in molecular weight is due to processing to polylactosaminoglycan [2].
• Cell fractionation and protein solubility studies indicate NB is an integral membrane protein, and NB has been shown to be a dimer under nonreducing conditions [3].
• Thus, the NB protein is not essential for influenza B virus replication in cell culture but promotes efficient growth in mice [6].

References