The solution structure of the Sac7d/DNA complex: a small-angle X-ray scattering study.

Area of Science:

• Structural biology
• Biophysics
• Molecular biology

Background:

• Archaeal chromatin proteins play a role in DNA organization.
• Sac7d is a small, abundant DNA-binding protein found in archaea.
• Understanding DNA-protein interactions is crucial for deciphering genome structure and function.

Purpose of the Study:

• To investigate the structural organization of multimeric complexes formed between Sac7d and double-stranded DNA.
• To determine the DNA conformation induced by Sac7d binding in solution.
• To build and validate molecular models of Sac7d/DNA complexes.

Main Methods:

• Small-angle X-ray scattering (SAXS) was employed to study Sac7d/DNA complexes.
• Molecular modeling was used to generate and refine structural models.
• SAXS data and simulated scattering curves were used to validate models.

Main Results:

• Sac7d binds along the surface of an extended DNA structure.
• Models indicate DNA consists of B-DNA segments with sharp kinks at protein binding sites.
• DNA conformation features base pair tilting and a significant bending angle (approx. 70 degrees) at kink sites.
• Regularly repeating bends create a zigzag DNA structure with minimal compaction.
• Sac7d molecules form a unique structure with two left-handed helical ribbons around the DNA.

Conclusions:

• Sac7d binding induces significant local DNA bending, leading to a regularly kinked, zigzag structure.
• The overall DNA structure is extended, with negligible compaction, differing from some other DNA-binding proteins.
• The findings provide insights into the structural basis of DNA organization by archaeal chromatin proteins.