Host Cell Calpains Can Cleave Structural Proteins from the Enterovirus Polyprotein

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• Enteroviruses are RNA viruses causing diverse illnesses.
• Viral proteins are synthesized as a polyprotein, requiring cleavage by viral proteases.
• The role of cellular proteases in this process is not fully understood.

Purpose of the Study:

• To investigate the potential role of cellular calpains in enterovirus polyprotein processing.
• To determine if calpains can cleave enterovirus structural proteins.

Main Methods:

• In vitro assays using purified calpains 1 and 2.
• Western blotting to detect capsid protein release (VP1, VP3).
• Calpain inhibitor assays, calcium concentration dependence studies, peptide competition assays, and mass spectrometry.

Main Results:

• Calpains 1 and 2 increased the release of VP1 and VP3 capsid proteins from enterovirus B species P1 in vitro.
• Cleavage was calcium-dependent and inhibited by a calpain inhibitor.
• Calpains cleaved the VP3-VP1 interface, distinct from viral protease 3C's site.
• Calpains did not cleave between P1 and 2A.

Conclusions:

• Cellular calpains demonstrate in vitro capability to cleave structural proteins from enterovirus polyproteins.
• The in vivo relevance of calpain-mediated polyprotein processing in infected cells warrants further study.