Structural insights into substrate selectivity of ribosomal RNA methyltransferase RlmCD

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Ribosomal RNA (rRNA) modifications are essential for ribosome biogenesis and function.
• The methyltransferase RlmCD modifies 23S rRNA at specific sites (U747 and U1939) in Streptococcus pneumoniae.
• Understanding RlmCD's structure and function is key to elucidating bacterial rRNA modification pathways.

Purpose of the Study:

• To determine the high-resolution crystal structures of apo-form RlmCD and its complex with S-adenosylhomocysteine (SAH).
• To identify crucial residues involved in the catalytic activity of RlmCD using in-vitro assays.
• To elucidate the structural basis for RlmCD's substrate selectivity by comparing it with its homologue, RumA.

Main Methods:

• X-ray crystallography to obtain high-resolution structures of RlmCD.
• In-vitro methyltransferase assays to investigate enzyme activity and identify key residues.
• Comparative structural analysis between RlmCD and RumA.

Main Results:

• High-resolution crystal structures of apo-RlmCD and RlmCD-SAH complex were determined.
• Crucial residues for RlmCD's catalytic function were identified through in-vitro assays.
• A unique long linker in RlmCD's central domain was implicated as the determinant of its substrate selectivity, distinguishing it from RumA.

Conclusions:

• The structural and functional characterization of RlmCD provides insights into bacterial rRNA modification.
• The unique linker region in RlmCD is critical for its specific recognition of rRNA substrates.
• This research contributes to understanding the diversity and regulation of methyltransferase enzymes involved in ribosome function.