Preliminary X-ray diffraction studies of an RNA pseudoknot that inhibits HIV-1 reverse transcriptase

Area of Science:

• Structural biology
• Biochemistry
• Molecular biology

Background:

• Pseudoknot RNA structures are crucial for various biological processes, including gene regulation and viral replication.
• Determining the three-dimensional structure of RNA is essential for understanding its function at a molecular level.

Purpose of the Study:

• To obtain high-quality crystals of a 26-nucleotide pseudoknot RNA (PK26) suitable for X-ray diffraction.
• To establish a robust crystallization protocol for pseudoknot RNAs.
• To prepare heavy-atom derivatives for structure determination.

Main Methods:

• Phosphoramidite chemistry for RNA synthesis.
• Denaturing polyacrylamide gel electrophoresis for purification.
• X-ray crystallography for structural analysis.
• Multiple isomorphous replacement (MIR) for phase determination.

Main Results:

• Successfully grown crystals of PK26 RNA.
• Crystals belong to space group P4(1)22 or P4(3)22 with unit-cell dimensions a = b = 61.6, c = 98.9 A.
• Diffraction data were collected to 2.9 A resolution.
• Crystallization proved robust to variations in nucleotide length and salt concentration.
• Brominated derivatives were synthesized and crystallized for MIR phasing.

Conclusions:

• The developed crystallization method is effective for obtaining diffraction-quality crystals of pseudoknot RNAs.
• The obtained crystals and derivatives pave the way for determining the high-resolution structure of PK26 RNA.
• Understanding the structure of PK26 RNA will provide insights into its biological role and potential therapeutic applications.