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Extracellular truncated influenza virus nucleoprotein
E N Prokudina1, N P Semenova, V M Chumakov
1The D. I. Ivanovsky Institute of Virology, 123098 Gamaleya 16, Moscow, Russia.
Abstract:
In the culture medium of MDCK cells infected with influenza A/Duck/Ukraine/1/63(H3N8) virus two kinds of virus nucleoprotein (NP) are detected: full-length 56 kDa NP and truncated 53 kDa NP. However, in infected cells 53 kDa NP may be detected only at short pulse and after 10 min chase it becomes nondetectable. The extracellular truncated 53 kDa NP is detected in free RNP, and not in the virions. Both extracellular free 53 and 56 kDa NP in the virions are completely oligomerized. Several data argue against the possibility of extracellular 53 kDa NP formation being a result of extracellular 56 kDa NP proteolytic degradation. Thus, the accumulation of extracellular 53 kDa NP takes place only in the course of infection, and the amount of 53 kDa NP is not increased during prolonged storage of cell-free culture medium at +37 degrees C. Moreover, all extracellular 56 kDa NP of A/Duck/Ukraine/1/63 influenza virus is present in the oligomeric form, and the latter, in contrast to the mononeric form, is highly resistant to proteases. The possibility is discussed that in the course of A/Duck/Ukraine/1/63 (H3N8) influenza virus infection a fraction of the synthesized 56 kDa monomeric NP undergoes the proteolytic cleavage in the infected cells before oligomerization and forms the 53 kDa NP. This 53 kDa NP is then oligomerized, enters the RNP and is quickly secreted from the cells.
Insights
Influenza A virus infection produces two nucleoproteins (NP): full-length 56 kDa and truncated 53 kDa. The 53 kDa NP is secreted from infected cells and found in ribonucleoprotein complexes.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Influenza A virus infection involves the synthesis and assembly of viral components, including the nucleoprotein (NP).
- The behavior and fate of viral proteins during infection are crucial for understanding viral replication and pathogenesis.
Purpose of the Study:
- To investigate the characteristics and origins of two distinct influenza A virus nucleoprotein (NP) forms (56 kDa and 53 kDa) observed during MDCK cell infection.
- To elucidate the processing, localization, and secretion pathways of the truncated 53 kDa NP.
Main Methods:
- Infection of Madin-Darby canine kidney (MDCK) cells with influenza A/Duck/Ukraine/1/63 (H3N8) virus.
- Detection and characterization of viral nucleoproteins (NP) in infected cells and culture medium using techniques like pulse-chase analysis.
- Analysis of NP oligomerization state and association with ribonucleoprotein (RNP) complexes.
Main Results:
- Two NP forms, full-length 56 kDa and truncated 53 kDa, were detected in the culture medium of infected MDCK cells.
- The 53 kDa NP was transiently detected within infected cells but was found extracellularly in free RNP complexes, not within virions.
- Extracellular NPs (both 53 kDa and 56 kDa) were oligomerized, with the 56 kDa form showing high protease resistance in its oligomeric state.
Conclusions:
- The 53 kDa NP is likely formed intracellularly through proteolytic cleavage of the 56 kDa NP monomer before oligomerization.
- This truncated NP then oligomerizes, incorporates into RNPs, and is rapidly secreted from infected cells.
- The findings suggest a specific pathway for the processing and secretion of a fraction of influenza NP during infection.