Crystal structure of Middle East respiratory syndrome coronavirus helicase

Hao, Wei; Wojdyla, Justyna Aleksandra; Zhao, Rong; Han, Ruiyun; Das, Rajat; Zlatev, Ivan; Manoharan, Muthiah; Wang, Meitian; Cui, Sheng

CoV helicase is one of the three evolutionary most conserved proteins in nidoviruses [27] , thus making it an important target for drug development [28] . Previous biochemical characterizations have shown that CoV nsp13 exhibits multiple enzymatic activities, which include hydrolysis of NTPs and dNTPs, unwinding of DNA and RNA duplexes with 5'-3' directionality and the RNA 5'-triphosphatase activity [29, 30] . Additionally, the RNA dependent RNA polymerase (RdRP, nsp12) of CoV physically interacts with nsp13 and enhances its unwinding activity [31] . Although the molecular mechanism underlying these activities and the role of nsp13 in viral RNA synthesis are poorly understood, mutagenesis studies have identified a collection of residues important for the activity of nidovirus helicase. Disruption of the zinc binding function of 229E-CoV nsp13 or EAV nsp10 by replacing the conserved Cys/His residues at ZBD or deleting the entire zinc binding domain interfere with the ATPase activity of the helicases. Moreover, the activity of nsp10 is not complemented by providing wild-type ZBD in trans [32] . These results suggest that ZBD of nidovirus helicase modulates the ATPase/helicase activity in cis. CoVs nsp13 is essential for virus replication. ATPase/helicase deficient mutations of nsp13 (either at the zinc-binding site or the Walker A motif) can lead to the abolition of CoV replication. The mouse hepatitis virus (MHV) M protein and nsp13 are required for efficient replication An A335V mutation in the helicase core of nsp13 causes the attenuation of MHV replication both in vitro and in vivo [33] .