Protein oxidation increases SAMHD1 binding ssDNA via its regulatory site.

Area of Science:

• Molecular Biology
• Biochemistry
• Cell Biology

Background:

• Sterile alpha motif and histidine-aspartate domain containing protein 1 (SAMHD1) is a key enzyme with dNTP hydrolase activity.
• SAMHD1 plays crucial roles in viral restriction, cell cycle regulation, and innate immunity.
• A novel dNTPase-independent function in homologous recombination (HR) repair of DNA double-strand breaks has been recently identified for SAMHD1.

Purpose of the Study:

• To investigate the role of post-translational modifications, specifically oxidation, on SAMHD1 function.
• To elucidate the mechanism by which SAMHD1 participates in DNA repair pathways.
• To determine the structural basis for oxidized SAMHD1 interaction with single-stranded DNA (ssDNA).

Main Methods:

• Biochemical assays to assess SAMHD1 activity and ssDNA binding affinity.
• Cell cycle analysis to determine the timing of SAMHD1 oxidation.
• X-ray crystallography to determine the structure of oxidized SAMHD1 in complex with ssDNA.

Main Results:

• Oxidation of SAMHD1 significantly increases its affinity for ssDNA.
• SAMHD1 oxidation occurs in a cell cycle-dependent manner, specifically during the S phase.
• The crystal structure reveals that oxidized SAMHD1 binds ssDNA at regulatory sites located at the dimer interface.

Conclusions:

• Oxidation of SAMHD1 acts as a regulatory switch, modulating its function between dNTPase activity and DNA binding.
• The cell cycle-dependent oxidation and ssDNA binding suggest a role for SAMHD1 in homologous recombination repair.
• Structural insights provide a mechanistic understanding of how SAMHD1's DNA binding is regulated by oxidation.