A unique RNA Fold in the RumA-RNA-cofactor ternary complex contributes to substrate selectivity and enzymatic...

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Ribosomal RNA (rRNA) modification is crucial for protein synthesis.
• RumA is the specific enzyme responsible for methylating U1939 in E. coli 23S rRNA.
• Understanding enzyme-substrate interactions is key to elucidating catalytic mechanisms.

Purpose of the Study:

• To determine the structural basis for RumA's unique selectivity in methylating E. coli 23S rRNA.
• To uncover the mechanism by which the RNA substrate actively participates in catalysis.
• To explore potential evolutionary insights into early RNA-protein interactions.

Main Methods:

• X-ray crystallography to determine the structure of the RumA/RNA/S-adenosylhomocysteine complex.
• Structural analysis to identify key RNA-enzyme interactions and conformational changes.
• Biochemical assays to assess catalytic efficiency and substrate binding.

Main Results:

• The structure reveals that RumA "refolds" the single-stranded RNA substrate into a compact conformation.
• A second base is "flipped out" to interact with the S-adenosylhomocysteine cofactor, while permuted nucleotides fill the vacated site.
• The 3' hairpin of the RNA binds distally, contributing binding energy and enhancing catalytic efficiency.

Conclusions:

• RumA achieves unique selectivity through extensive RNA refolding and specific base interactions.
• The RNA substrate plays an active role in the catalytic mechanism, not just as a passive target.
• The findings suggest that RumA and its RNA substrate may represent an ancient form of RNA-protein collaboration.