Cryo-EM structures of Uba7 reveal the molecular basis for ISG15 activation and E1-E2 thioester transfer

Mohammad Afsar, GuanQun Liu, Lijia Jia, Eliza A. Ruben, Digant Nayak, Zuberwasim Sayyad, Priscila dos Santos Bury, Kristin E. Cano, Anindita Nayak, Xiang Ru Zhao, Ankita Shukla, Patrick Sung, Elizabeth V. Wasmuth, Michaela U. Gack and Shaun K. Olsen ()
Additional contact information
Mohammad Afsar: University of Texas Health Science Center at San Antonio
GuanQun Liu: Cleveland Clinic
Lijia Jia: University of Texas Health Science Center at San Antonio
Eliza A. Ruben: University of Texas Health Science Center at San Antonio
Digant Nayak: University of Texas Health Science Center at San Antonio
Zuberwasim Sayyad: Cleveland Clinic
Priscila dos Santos Bury: University of Texas Health Science Center at San Antonio
Kristin E. Cano: University of Texas Health Science Center at San Antonio
Anindita Nayak: University of Texas Health Science Center at San Antonio
Xiang Ru Zhao: University of Texas Health Science Center at San Antonio
Ankita Shukla: University of Texas Health Science Center at San Antonio
Patrick Sung: University of Texas Health Science Center at San Antonio
Elizabeth V. Wasmuth: University of Texas Health Science Center at San Antonio
Michaela U. Gack: Cleveland Clinic
Shaun K. Olsen: University of Texas Health Science Center at San Antonio

Nature Communications, 2023, vol. 14, issue 1, 1-14

Abstract: Abstract ISG15 plays a crucial role in the innate immune response and has been well-studied due to its antiviral activity and regulation of signal transduction, apoptosis, and autophagy. ISG15 is a ubiquitin-like protein that is activated by an E1 enzyme (Uba7) and transferred to a cognate E2 enzyme (UBE2L6) to form a UBE2L6-ISG15 intermediate that functions with E3 ligases that catalyze conjugation of ISG15 to target proteins. Despite its biological importance, the molecular basis by which Uba7 catalyzes ISG15 activation and transfer to UBE2L6 is unknown as there is no available structure of Uba7. Here, we present cryo-EM structures of human Uba7 in complex with UBE2L6, ISG15 adenylate, and ISG15 thioester intermediate that are poised for catalysis of Uba7-UBE2L6-ISG15 thioester transfer. Our structures reveal a unique overall architecture of the complex compared to structures from the ubiquitin conjugation pathway, particularly with respect to the location of ISG15 thioester intermediate. Our structures also illuminate the molecular basis for Uba7 activities and for its exquisite specificity for ISG15 and UBE2L6. Altogether, our structural, biochemical, and human cell-based data provide significant insights into the functions of Uba7, UBE2L6, and ISG15 in cells.

Date: 2023
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DOI: 10.1038/s41467-023-39780-z

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