Conformation-based refinement of 18-mer DNA structures

Area of Science:

• Structural Biology
• Biochemistry
• Genomics

Background:

• Bacterial repetitive extragenic palindromes (REPs) are DNA sequences with potential regulatory roles.
• Understanding the structural basis of DNA conformation is crucial for deciphering gene regulation.
• CG-rich DNA sequences can adopt non-canonical structures.

Purpose of the Study:

• To determine the crystal structures of CG-rich DNA 18-mers with systematic mutations.
• To investigate the structural behavior of these DNA sequences in solution and in crystalline form.
• To develop and validate a novel structure refinement protocol for low-resolution data.

Main Methods:

• X-ray crystallography was used to obtain nine new crystal structures of DNA 18-mers.
• Systematic mutation of the central dinucleotide (XZ) to all 16 possible sequences.
• Development and application of a dinucleotide conformer (NtC) class-driven refinement protocol.
• A novel validation method comparing electron density and conformational similarity was employed.

Main Results:

• Ten DNA 18-mers crystallized as A-form duplexes.
• The NtC-driven refinement protocol significantly stabilized structure refinement, especially in regions of poor electron density.
• The developed protocol is adaptable to other low-resolution structural data, including cryo-electron microscopy (cryo-EM) maps.
• A novel validation method was successfully used to assess the quality of the final structural models.

Conclusions:

• The study provides new insights into the structural diversity of CG-rich DNA relevant to bacterial REPs.
• The NtC-driven refinement protocol offers a robust method for improving structure determination from low-resolution data.
• The findings contribute to the understanding of DNA structure-function relationships and structural biology methodologies.