Key result
Deletion of the N-terminal amphipathic helix of FMDV 2C yields a soluble protein that exhibits ATPase and RNA binding activity and forms hexameric ring structures in the presence of ATP and RNA.
FMDV 2C protein forms hexameric ring structures characteristic of AAA+ ATPases and utilizes a coordinated mechanism for ATP hydrolysis, providing structural insights into picornavirus replication.
Hypothesis-generating for picornavirus replication mechanisms; leaves open in vivo validation and therapeutic targeting.
Foot-and-mouth disease virus (FMDV), a positive sense, single-stranded RNA virus, causes a highly contagious disease in cloven-hoofed livestock. Like other picornaviruses, FMDV has a conserved 2C protein assigned to the superfamily 3 helicases a group of AAA+ ATPases that has a predicted N-terminal membrane-binding amphipathic helix attached to the main ATPase domain. In infected cells, 2C is involved in the formation of membrane vesicles, where it co-localizes with viral RNA replication complexes, but its precise role in virus replication has not been elucidated. We show here that deletion of the predicted N-terminal amphipathic helix enables overexpression in Escherichia coli of a highly soluble truncated protein, 2C(34-318), that has ATPase and RNA binding activity. ATPase activity was abrogated by point mutations in the Walker A (K116A) and B (D160A) motifs and Motif C (N207A) in the active site. Unliganded 2C(34-318) exhibits concentration-dependent self-association to yield oligomeric forms, the largest of which is tetrameric. Strikingly, in the presence of ATP and RNA, FMDV 2C(34-318) containing the N207A mutation, which binds but does not hydrolyze ATP, was found to oligomerize specifically into hexamers. Visualization of FMDV 2C-ATP-RNA complexes by negative stain electron microscopy revealed hexameric ring structures with 6-fold symmetry that are characteristic of AAA+ ATPases. ATPase assays performed by mixing purified active and inactive 2C(34-318) subunits revealed a coordinated mechanism of ATP hydrolysis. Our results provide new insights into the structure and mechanism of picornavirus 2C proteins that will facilitate new investigations of their roles in infection.
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Sweeney et al. (2010) studied Foot-and-mouth disease virus (FMDV). Deletion of N-terminal amphipathic helix and point mutations in FMDV 2C protein was evaluated on ATPase activity, RNA binding, and oligomerization state. Deletion of the N-terminal amphipathic helix of FMDV 2C yields a soluble protein that exhibits ATPase and RNA binding activity and forms hexameric ring structures in the presence of ATP and RNA.
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