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Open AccessArticle

Host Cell Calpains Can Cleave Structural Proteins from the Enterovirus Polyprotein

1
Department of Biological and Environmental Science/Nanoscience center, University of Jyväskylä, Survontie 9C, FI-40500 Jyväskylä, Finland
2
Faculty of Medicine and Health Technology, Tampere University, FI-33014 Tampere, Finland
3
Department of Clinical Chemistry, Fimlab Laboratories, Pirkanmaa Hospital District, FI-33520 Tampere, Finland
*
Author to whom correspondence should be addressed.
Viruses 2019, 11(12), 1106; https://doi.org/10.3390/v11121106
Received: 8 November 2019 / Revised: 26 November 2019 / Accepted: 26 November 2019 / Published: 28 November 2019
(This article belongs to the Special Issue Human Picornaviruses)
Enteroviruses are small RNA viruses that cause diseases with various symptoms ranging from mild to severe. Enterovirus proteins are translated as a single polyprotein, which is cleaved by viral proteases to release capsid and nonstructural proteins. Here, we show that also cellular calpains have a potential role in the processing of the enteroviral polyprotein. Using purified calpains 1 and 2 in an in vitro assay, we show that addition of calpains leads to an increase in the release of VP1 and VP3 capsid proteins from P1 of enterovirus B species, detected by western blotting. This was prevented with a calpain inhibitor and was dependent on optimal calcium concentration, especially for calpain 2. In addition, calpain cleavage at the VP3-VP1 interface was supported by a competition assay using a peptide containing the VP3-VP1 cleavage site. Moreover, a mass spectrometry analysis showed that calpains can cleave this same peptide at the VP3-VP1 interface, the cutting site being two amino acids aside from 3C’s cutting site. Furthermore, we show that calpains cannot cleave between P1 and 2A. In conclusion, we show that cellular proteases, calpains, can cleave structural proteins from enterovirus polyprotein in vitro. Whether they assist polyprotein processing in infected cells remains to be shown.
Keywords: enterovirus; calpain; proteolytic processing; RNA virus; polyprotein enterovirus; calpain; proteolytic processing; RNA virus; polyprotein
MDPI and ACS Style

Laajala, M.; Hankaniemi, M.M.; Määttä, J.A.E.; Hytönen, V.P.; Laitinen, O.H.; Marjomäki, V. Host Cell Calpains Can Cleave Structural Proteins from the Enterovirus Polyprotein. Viruses 2019, 11, 1106.

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