Structures of kobuviral and siciniviral polymerases reveal conserved mechanism of picornaviral polymerase activation

• Published in: Journal of structural biology Vol. 208; no. 2; pp. 92 - 98
• Main Authors: Dubankova, Anna, Horova, Vladimira, Klima, Martin, Boura, Evzen
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-11-2019
• Subjects: Crystal structure; Kobuvirus; Picornavirus; Polymerase; RNA; Polymerase; Picornavirus; RNA; Kobuvirus; Crystal structure
• ISSN: 1047-8477; 1095-8657
• DOI: 10.1016/j.jsb.2019.08.004

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•Picornaviral RNA genome serves as messenger RNA and is directly transcribed into a single polyprotein chain.•The RNA-dependent RNA polymerase 3Dpol, arises from a stable 3CDpro precursor that has high proteolytical but no polymerase activity.•Several mechanisms of how cleavage of the 3CD precursor activates the polymerase activity were suggested.•We have solved two crystal structures of atypical picornaviral polymerases that have a serine at the first position where other picornaviruses have a glycine residue.•The structures reveal a common mechanism of 3Dpol activation for all picornaviral polymerases that lies in the stabilization of the α10 helix.
RNA-dependent RNA polymerase 3Dpol is a key enzyme for the replication of picornaviruses. The viral genome is translated into a single polyprotein that is subsequently proteolytically processed into matured products. The 3Dpol enzyme arises from a stable 3CD precursor that has high proteolytic activity but no polymerase activity. Upon cleavage of the precursor the newly established N-terminus of 3Dpol is liberated and inserts itself into a pocket on the surface of the 3Dpol enzyme. The essential residue for this mechanism is the very first glycine that is conserved among almost all picornaviruses. However, kobuviruses and siciniviruses have a serine residue instead. Intrigued by this anomaly we sought to solve the crystal structure of these 3Dpol enzymes. The structures revealed a unique fold of the 3Dpol N-termini but the very first serine residues were inserted into a charged pocket in a similar manner as the glycine residue in other picornaviruses. These structures revealed a common underlying mechanism of 3Dpol activation that lies in activation of the α10 helix containing a key catalytical residue Asp238 that forms a hydrogen bond with the 2′ hydroxyl group of the incoming NTP nucleotide.