2Q6G:
reference: Structures of two coronavirus main proteases: implications for substrate binding and antiviral drug design., Xue X, Yu H, Yang H, Xue F, Wu Z, Shen W, Li J, Zhou Z, Ding Y, Zhao Q, Zhang XC, Liao M, Bartlam M, Rao Z, J Virol. 2008 Mar;82(5):2515-27. Epub 2007 Dec 19. PMID: 18094151

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