The Enzymatic Mechanism of OAS: How Metal Ions and Quantum Effects Help Activate Innate Immunity

Area of Science:

• Biochemistry
• Immunology
• Structural Biology

Background:

• 2'-5'-Oligoadenylate synthetases (OAS) are critical innate immune sensors detecting viral double-stranded RNA to initiate antiviral responses.
• Understanding the molecular mechanisms of OAS is essential for developing novel immunomodulatory therapies.

Purpose of the Study:

• To elucidate the detailed enzymatic mechanism of OAS using integrated structural, kinetic, and quantum chemical analyses.
• To investigate the role of metal ions and quantum effects in OAS catalysis.

Main Methods:

• X-ray crystallography of OAS1 postreactive complexes.
• Kinetic analyses.
• Quantum chemical calculations.

Main Results:

• Detailed geometry of OAS1 post-product formation and dissociation.
• Elucidation of sequential product release and the role of divalent metal ions.
• Identification of a potential transient role for a third metal ion in catalysis.
• Demonstration of quantum mechanisms' central role in OAS function.
• Observation that Mn2+ substitution for Mg2+ enhances substrate binding and OAS activity 9-fold.

Conclusions:

• The study provides unprecedented insights into the OAS enzymatic mechanism, including metal ion coordination and quantum effects.
• Findings are relevant to the OAS/cGAS family and nucleotidyltransferases, with potential therapeutic implications.