stalk domain of coronavirus Nsp13 helicase and related proteins
This model represents the stalk domain of coronavirus non-structural protein 13 (Nsp13) helicase, found in the Nsp3s of alpha-, beta-, gamma-, and deltacoronaviruses, including Severe Acute Respiratory Syndrome coronavirus (SARS-CoV), SARS-CoV-2 (also called 2019 novel CoV or 2019-nCoV), and Middle East respiratory syndrome coronavirus (MERS-CoV). Helicases are classified based on the arrangement of conserved motifs into six superfamilies; coronavirus helicases in this family belong to superfamily 1 (SF1). Helicases catalyze NTP-dependent unwinding of nucleic acid duplexes into single strands. Nsp13 is a component of the viral RNA synthesis replication and transcription complex (RTC). It consists of an N-terminal ZBD (Cys/His rich zinc-binding domain), a stalk domain, a 1B regulatory domain, and SF1 helicase core. The stalk domain lies between the ZBD domain and the 1B domain; a short loop connects the ZBD to the stalk domain. The stalk domain is comprised of three tightly-interacting alpha-helices connected to the 1B domain, transferring the effect from the ZBD domain onto the helicase core domains. The ZBD and stalk domains are critical for the helicase activity of SARS-CoV Nsp13.