The GlcN6P cofactor plays multiple catalytic roles in the glmS ribozyme

Area of Science:

• Biochemistry
• Molecular Biology
• RNA Catalysis

Background:

• RNA enzymes (ribozymes) exhibit diverse functions but limited chemical diversity.
• Protein enzymes utilize cofactors to enhance reactivity.
• The glmS ribozyme naturally employs the glucosamine-6-phosphate (GlcN6P) organic cofactor for phosphodiester bond cleavage.

Purpose of the Study:

• To elucidate the multifaceted catalytic roles of the GlcN6P cofactor in the glmS ribozyme.
• To investigate the chemical mechanisms underlying GlcN6P-mediated phosphodiester bond cleavage.
• To understand how organic cofactors expand the catalytic repertoire of ribozymes.

Main Methods:

• Stereospecific normal and inverse thio effect experiments.
• Metal-ion rescue assays in both holoribozyme and aporibozyme systems.
• Computational calculations to support experimental findings.

Main Results:

• Large stereospecific normal thio effects and lack of metal-ion rescue in the holoribozyme indicate direct chemical roles for nucleobases and GlcN6P.
• GlcN6P acts as a general acid and aligns the active site for self-cleavage.
• Large stereospecific inverse thio effects in the aporibozyme show GlcN6P disrupts inhibitory nucleophile interactions.
• Strong metal-ion rescue in the aporibozyme demonstrates GlcN6P provides electrostatic stabilization.

Conclusions:

• Organic cofactors like GlcN6P enable ribozymes to perform diverse catalytic functions beyond their inherent chemical limitations.
• GlcN6P plays multiple direct chemical and stabilizing roles in glmS ribozyme catalysis.
• RNA cofactors are essential for expanding the functional diversity of RNA enzymes.