1B domain of coronavirus SARS NSP13 helicase and related proteins
Helicases catalyze NTP-dependent unwinding of nucleic acid duplexes into single strands and are classified based on the arrangement of conserved motifs into six superfamilies. Members of this subfamily belong to helicase superfamily 1 (SF1) and include coronavirus helicases such as Severe Acute Respiratory Syndrome coronavirus (SARS) non-structural protein 13 (SARS-Nsp13). SARS-Nsp13 is a component of the viral RNA synthesis replication and transcription complex (RTC). Structural studies of a stable RTC which included the RNA-dependent RNA polymerase holoenzyme (Nsp7, two molecules of Nsp82, Nsp12), two molecules of Nsp13 helicase accessory factor and an RNA template product suggests that the Nsp13 helicase may drive RTC backtracking, affecting proofreading and template switching. SARS-Nsp13 is a multidomain protein; its other domains include an N-terminal Cys/His rich zinc-binding domain (CH/ZBD) and a SF1 helicase core. The 1B domain is involved in nucleic acid substrate binding; the 1B domain of the related Equine arteritis virus (EAV) Nsp10 undergoes large conformational change upon substrate binding, and together with the 1A and 2A domains of the helicase core form a channel that accommodates the single stranded nucleic acids.
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