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

Prior to crystallization trials nsp13 protein was incubated with a 5'-triphosphate singlestranded DNA containing 15T (ppp-15T). Highly redundant multi-wavelength anomalous diffraction data were collected using the X-ray with wavelengths close to the absorption edge of zinc (Hrem: 1.2810Ã…, Peak: 1.2827Ã… and Infl: 1.2831Ã…). Crystal belonged to the space group P6 1 22, and contained two molecules per ASU. An interpretable electron density map was calculated using SHARP/autoSHARP [41] . An initial model of MERS-CoV nsp13 was manually built using Coot [42] . Finally, a native data with highest resolution (3.0Ã…) was collected using the X-rays with the wavelength of 0.978Ã…. Higher resolution structure was solved by molecular replacement using the initial nsp13 structure as the searching model. The 3.0Ã… structure was refined using PHENIX [43] . In the final model, 145-230aa (the entire 1B domain) of molecule A are disordered, probably due to mobility of 1B and the lack of crystal contacts, whereas in molecule B, 591 out of 598 amino acids were located in the electron density maps (S4 Fig).