Structural basis of the monkeypox virus mRNA cap N7 methyltransferase complex

Area of Science:

• Virology
• Structural Biology
• Biochemistry

Background:

• Mpox, caused by MPXV, is a significant global health concern.
• MPXV's mRNA cap N7 methyltransferase (RNMT) is crucial for evading host antiviral responses.
• MPXV RNMT comprises large (E1) and small (E12) subunits, with their assembly mechanism previously unknown.

Purpose of the Study:

• To elucidate the structural basis of MPXV RNMT assembly and function.
• To investigate the role of subunits E1 and E12 in MPXV RNMT activity.
• To identify potential targets for anti-Mpox virus inhibitors.

Main Methods:

• X-ray crystallography was used to determine the structures of E12, E1_CTD-E12 complex, and the E1_CTD-E12-SAM ternary complex.
• Functional studies were performed to assess the role of specific residues and subunits.
• Comparative structural analysis with homologous vaccinia virus (VACV) D1-D12 complex and AlphaFold2 predictions were conducted.

Main Results:

• Crystal structures revealed detailed conformations of MPXV E12, E1_CTD-E12 complex, and the ternary complex.
• The N-terminal extension of E1_CTD and subunit E12 are critical for SAM binding.
• Structural comparisons suggest an allosteric activation mechanism of E1 by E12 in MPXV, similar to VACV D1-D12.

Conclusions:

• The study provides the first structural insights into the MPXV RNMT E1-E12 complex assembly and activation.
• The findings reveal critical interfaces for SAM binding and potential targets for antiviral drug discovery.
• Understanding the structural basis of MPXV RNMT activity can guide the development of novel anti-Mpox virus therapeutics.