Crystal structure of the shutoff and exonuclease protein from the oncogenic Kaposi's sarcoma-associated herpesvirus

Area of Science:

• Virology
• Structural Biology
• Molecular Biology

Background:

• Kaposi's sarcoma-associated herpesvirus (KSHV) protein SOX and Epstein-Barr virus (EBV) BGLF5 are early lytic phase alkaline nucleases.
• These proteins possess dual functions: viral DNA maturation and host mRNA degradation (host shutoff).

Purpose of the Study:

• To determine the crystal structure of KSHV SOX protein.
• To elucidate the structural basis for its enzymatic activities and biological functions.

Main Methods:

• X-ray crystallography to determine the 1.85 Å crystal structure of SOX.
• DNA binding modeling and mutagenesis studies.
• Oligonucleotide binding assays.

Main Results:

• The crystal structure of SOX was determined at 1.85 Å resolution.
• Identified catalytic residues responsible for 5 eal-exonuclease activity and a crevice for duplex DNA binding, suggesting a role in viral DNA recombination.
• Mutations affecting host shutoff localized to the N-terminal domain, indicating involvement in protein-protein interactions and mRNA degradation pathways.

Conclusions:

• The SOX crystal structure provides insights into the bifunctional nature of herpesvirus alkaline nucleases.
• Structural data supports SOX's role in viral DNA processing and host shutoff mechanisms.
• SOX's N-terminal domain is crucial for host shutoff, likely through interactions mediating RNase activity.