2NVU:
reference: Basis for a ubiquitin-like protein thioester switch toggling E1-E2 affinity., Huang DT, Hunt HW, Zhuang M, Ohi MD, Holton JM, Schulman BA, Nature. 2007 Jan 25;445(7126):394-8. Epub 2007 Jan 14. PMID: 17220875

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