Structure of the most conserved internal loop in SRP RNA

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Signal recognition particle (SRP) is crucial for protein targeting to membranes.
• In prokaryotes, SRP comprises SRP RNA and SRP54, which binds nascent proteins.
• SRP54 interacts with signal sequences on proteins for translocation.

Purpose of the Study:

• To determine the solution NMR structure of a key 28-mer RNA region of SRP RNA.
• To elucidate the structural basis of SRP54 binding to SRP RNA.
• To understand the role of conserved bases in SRP function.

Main Methods:

• Solution Nuclear Magnetic Resonance (NMR) spectroscopy.
• Structural analysis of a 28-nucleotide RNA fragment.
• Investigating magnesium ion (Mg2+) dependent structural features.

Main Results:

• The 28-mer RNA forms a novel Mg2+-dependent structure.
• Unusual cross-strand interactions, including A/A stacking and G-phosphate hydrogen bonds, were identified.
• A six-nucleotide internal loop exhibits unique structural properties.

Conclusions:

• The determined RNA structure explains the phylogenetic conservation of loop bases.
• The findings highlight the structural importance of the loop for SRP54 binding.
• This structural insight is critical for understanding SRP-mediated protein targeting.