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Activation of Sendai virus infectivity by an enzyme in chicken amniotic fluid
Abstract:
Sendai virus grown in LLC-MK2 cells is known to have low infectivity, no detectable haemolysing ability and predominantly uncleaved F glycoprotein. Treatment of such virus with chicken amniotic fluid resulted in a 10(3)- to 10(4)-fold increase in infectivity, the development of haemolysing ability, and cleavage of the F glycoprotein. The 'Sendai activating enzyme' (SAE) responsible for these effects required the presence of 1 mM-Ca2+ ions for maximum activity. It was inhibited by phenylmethylsulphonyl fluoride and soybean trypsin inhibitor but was unaffected by sulphydryl-blocking agents. The results of gel filtration tests suggested that the molecular weight of SAE was about 55 000. SAE may be the natural proteolytic activator of Sendai virus in a soluble form.
Insights
Chicken amniotic fluid contains a Sendai activating enzyme (SAE) that significantly boosts Sendai virus infectivity and haemolysing ability by cleaving its F glycoprotein. This enzyme requires calcium ions for optimal activity.
Area of Science:
- Virology
- Molecular Biology
- Enzymology
Background:
- Sendai virus, when cultured in LLC-MK2 cells, exhibits low infectivity and lacks haemolysing ability.
- The F glycoprotein of this virus predominantly remains uncleaved, contributing to its reduced infectivity.
Purpose of the Study:
- To investigate the factors responsible for enhancing Sendai virus infectivity and haemolysing ability.
- To characterize the enzyme involved in the activation of Sendai virus.
Main Methods:
- Treatment of low-infectivity Sendai virus with chicken amniotic fluid.
- Assay of viral infectivity and haemolysing ability.
- Analysis of F glycoprotein cleavage.
- Enzyme characterization including ion dependency, inhibitor susceptibility, and molecular weight determination via gel filtration.
Main Results:
- Chicken amniotic fluid treatment increased Sendai virus infectivity by 10^3- to 10^4-fold.
- Treatment also induced haemolysing ability and F glycoprotein cleavage.
- The responsible enzyme, termed Sendai activating enzyme (SAE), requires Ca2+ for maximal activity, is inhibited by PMSF and soybean trypsin inhibitor, and has a molecular weight of approximately 55,000.
Conclusions:
- A soluble enzyme in chicken amniotic fluid, SAE, acts as a potent activator for Sendai virus.
- SAE likely functions as the natural proteolytic activator of Sendai virus, mediating F glycoprotein cleavage.