Characterization of the interactions between SIVrcm Vpx and red-capped mangabey SAMHD1

Area of Science:

• Virology
• Molecular Biology
• Immunology

Background:

• SAMHD1 (SAM domain- and HD domain-containing protein 1) is a key innate immune protein that restricts HIV-1 and SIV replication in myeloid cells and resting CD4+ T-cells.
• Certain SIV lineages, like SIVsm/SIVmac and SIVrcm, encode a Vpx protein that antagonizes SAMHD1.
• Vpx hijacks the host ubiquitin-proteasome system, recruiting a DCAF1-CUL4-DDB1 E3 ligase complex to polyubiquitinate and degrade SAMHD1.

Purpose of the Study:

• To characterize the molecular interactions underlying SIVrcm Vpx-mediated degradation of red-capped mangabey SAMHD1 (rcmSAMHD1).
• To elucidate the structural basis for the distinct interaction between SIVrcm Vpx and rcmSAMHD1 compared to SIVmac Vpx and human SAMHD1.
• To provide insights into the viral 'arms race' driving host-pathogen interactions.

Main Methods:

• Site-directed mutagenesis of SIVrcm Vpx and rcmSAMHD1.
• Molecular modeling of the rcmSAMHD1-NtD, Vpxrcm, and DCAF1-CtD complex.
• Biochemical assays to analyze protein-protein interactions and degradation.

Main Results:

• The W23LHR26 peptide of SIVrcm Vpx is crucial for recognizing rcmSAMHD1.
• Specific amino acids (Phe15, Leu36, Phe52, Arg55, Arg56) in the N-terminal domain (NtD) of rcmSAMHD1 mediate interaction with Vpxrcm.
• The interaction interface between rcmSAMHD1-NtD and Vpxrcm differs significantly from the human SAMHD1-CtD and Vpxsm interface.

Conclusions:

• SIVrcm Vpx and rcmSAMHD1 engage via a unique interface, distinct from the well-characterized SIVmac Vpx-human SAMHD1 interaction.
• These findings highlight the evolutionary adaptations in lentiviral Vpx proteins to overcome host restriction factors.
• The study deepens our understanding of virus-host co-evolution and the molecular mechanisms of viral antagonism.