Structural basis of transfer RNA processing by bacterial minimal RNase P

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Precursor tRNAs (pre-tRNAs) require precise processing of 5 -leader and 3 -trailer sequences for maturation and function.
• RNase P enzymes, responsible for 5 -leader removal, exist in various forms, including protein-only enzymes like HARP found in some bacteria and archaea.
• HARP enzymes form dodecamers, featuring multiple active sites, suggesting complex catalytic mechanisms.

Purpose of the Study:

• To elucidate the structure and function of HARP dodecamers in pre-tRNA maturation.
• To investigate the mechanism by which HARP recognizes and cleaves pre-tRNA substrates.
• To understand the evolutionary adaptation of small proteins through oligomerization for novel enzymatic functions.

Main Methods:

• Cryogenic electron microscopy (cryo-EM) to determine the structure of HARP dodecamers bound to pre-tRNAs.
• Biochemical assays to characterize the cleavage activities of HARP.
• Structural analysis to identify substrate recognition mechanisms.

Main Results:

• Cryo-EM structures revealed HARP dodecamers complexed with five distinct pre-tRNAs.
• HARP utilizes its oligomeric structure as a molecular ruler to recognize the invariant distance between the acceptor stem 5 -end and the T C-loop.
• Five active sites within the dodecamer are dedicated to 5 -leader cleavage, while the remaining seven sites exhibit 3 -trailer cleavage activity.

Conclusions:

• HARP dodecamerization is crucial for specific pre-tRNA recognition and efficient 5 -leader processing, demonstrating convergent evolution with other RNase P enzymes.
• The HARP dodecamer exhibits dual functionality, processing both 5 -leader and 3 -trailer sequences, a novel finding for this class of enzymes.
• This study highlights how protein oligomerization can drive the evolution of enzymatic function, enabling adaptation and acquisition of new roles in nucleic acid processing.