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Updated: May 26, 2026
Identifying Caspases and their Motifs that Cleave Proteins During Influenza A Virus Infection
Published on: July 21, 2022
Functional and biochemical characterization of the baculovirus caspase inhibitor MaviP35
I L Brand1, M M Green, S Civciristov
1Department of Biochemistry, La Trobe University, Bundoora, Victoria, Australia.
Abstract:
Many viruses express proteins which prevent the host cell death that their infection would otherwise provoke. Some insect viruses suppress host apoptosis through the expression of caspase inhibitors belonging to the P35 superfamily. Although a number of P35 relatives have been identified, Autographa californica (Ac) P35 and Spodoptera littoralis (Spli) P49 have been the most extensively characterized. AcP35 was found to inhibit caspases via a suicide substrate mechanism: the caspase cleaves AcP35 within its 'reactive site loop' then becomes trapped, irreversibly bound to the cleaved inhibitor. The Maruca vitrata multiple nucleopolyhedrovirus encodes a P35 family member (MaviP35) that exhibits 81% identity to AcP35. We found that this relative shared with AcP35 the ability to inhibit mammalian and insect cell death. Caspase-mediated cleavage within the MaviP35 reactive site loop occurred at a sequence distinct from that in AcP35, and the inhibitory profiles of the two P35 relatives differed. MaviP35 potently inhibited human caspases 2 and 3, DCP-1, DRICE and CED-3 in vitro, but (in contrast to AcP35) only weakly suppressed the proteolytic activity of the initiator human caspases 8, 9 and 10. Although MaviP35 inhibited the AcP35-resistant caspase DRONC in yeast, and was sensitive to cleavage by DRONC in vitro, MaviP35 failed to inhibit the proteolytic activity of bacterially produced DRONC in vitro.
Insights
Maruca vitrata multiple nucleopolyhedrovirus P35 (MaviP35) inhibits host cell death by targeting caspases. MaviP35 shows distinct inhibitory profiles compared to Autographa californica P35, affecting different caspases.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Viruses often encode proteins to prevent host cell apoptosis, aiding infection.
- Insect viruses utilize P35 superfamily caspase inhibitors to suppress host cell death.
- Autographa californica (Ac) P35 and Spodoptera littoralis (Spli) P49 are well-characterized viral caspase inhibitors.
Purpose of the Study:
- To characterize the functional properties of MaviP35, a P35 family member from Maruca vitrata multiple nucleopolyhedrovirus.
- To compare the caspase inhibitory activity and cleavage mechanisms of MaviP35 with the well-studied AcP35.
Main Methods:
- In vitro caspase inhibition assays using purified caspases and MaviP35.
- Analysis of MaviP35 cleavage sites by caspases.
- Functional assays in yeast to assess MaviP35's ability to inhibit specific caspases.
Main Results:
- MaviP35 effectively inhibits mammalian and insect cell death, similar to AcP35.
- Caspase-mediated cleavage of MaviP35 occurs at a different site than AcP35.
- MaviP35 potently inhibits executioner caspases (e.g., human caspases 2 and 3) but weakly inhibits initiator caspases (e.g., human caspases 8, 9, 10).
- MaviP35 inhibits the yeast caspase DRONC and is cleaved by it in vitro, but does not inhibit bacterially produced DRONC.
Conclusions:
- MaviP35 is a functional viral caspase inhibitor with distinct characteristics from AcP35.
- The differential inhibition profile suggests MaviP35 may target specific caspases involved in apoptosis pathways.
- Understanding MaviP35's mechanism provides insights into viral strategies for host immune evasion.
