Poliovirus 2C protein forms homo-oligomeric structures required for ATPase activity.
The poliovirus protein 2C plays an essential role in viral RNA replication, although its precise biochemical activities or structural requirements have not been elucidated. The protein has several distinctive properties, including ATPase activity and membrane and RNA binding, that are conserved among orthologs of many positive-strand RNA viruses. Sequence alignments have placed these proteins in the SF3 helicase family, a subset of the AAA+ ATPase superfamily. A feature common to AAA+ proteins is the formation of oligomeric rings that are essential for their catalytic functions. Here we show that a recombinant protein, MBP-2C, in which maltose-binding protein was fused to 2C, formed soluble oligomers and that ATPase activity was restricted to oligomer-containing fractions from gel-filtration chromatography. The active fraction was visualized by negative-staining electron microscopy as ring-like particles composed of 5-8 protomers. This conclusion was confirmed by mass measurements obtained by scanning transmission electron microscopy. Mutation of amino acid residues in the 2C nucleotide-binding domain demonstrated that loss of the ability to bind or hydrolyze ATP did not affect oligomerization. Co-expression of active MBP-2C and inactive mutant proteins generated mixed oligomers that exhibited little ATPase activity, suggesting that incorporation of inactive subunits eliminates the function of the entire particle. Finally, deletion of the N-terminal 38 amino acids blocked oligomerization of the fusion protein and eliminated ATPase activity, despite retention of an unaltered nucleotide-binding domain.
Adams
Peter
P
NIAID, Bethesda, Maryland 20892-8011.
Kandiah
Eaazhisai
E
NIAMS, National Institutes of Health, Bethesda, Maryland 20892-8011.
Effantin
Grégory
G
NIAMS, National Institutes of Health, Bethesda, Maryland 20892-8011.
Steven
Alasdair C
AC
NIAMS, National Institutes of Health, Bethesda, Maryland 20892-8011.
Ehrenfeld
Ellie
E
NIAID, Bethesda, Maryland 20892-8011.
D000251:Adenosine Triphosphatases / Q000737:chemistry*; D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000502:physiology*; D002850:Chromatography, Gel; D003432:Cross-Linking Reagents / Q000737:chemistry; D004789:Enzyme Activation; D015967:Gene Expression Regulation, Viral; D006868:Hydrolysis; D008855:Microscopy, Electron, Scanning / Q000379:methods; D046529:Microscopy, Electron, Transmission / Q000379:methods; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D017361:Viral Nonstructural Proteins / Q000737:chemistry / Q000502:physiology*
D002352:Carrier Proteins; D003432:Cross-Linking Reagents; D017361:Viral Nonstructural Proteins; C076023:2C protein, viral; D000251:Adenosine Triphosphatases