Structure and cellular dynamics of Deinococcus radiodurans single-stranded DNA (ssDNA)-binding protein (SSB)-DNA...

Area of Science:

• Microbiology
• Molecular Biology
• Structural Biology

Background:

• Deinococcus radiodurans is a bacterium known for its extreme radiation resistance.
• Single-stranded DNA-binding proteins (SSBs) are essential for DNA replication, repair, and recombination.
• DrSSB exhibits a rare homodimeric structure with two oligonucleotide-binding (OB) domains per monomer, unlike typical homotetrameric bacterial SSBs.

Purpose of the Study:

• To investigate the structural basis of ssDNA binding by DrSSB.
• To elucidate the biological functions of DrSSB in Deinococcus radiodurans radiation resistance.
• To understand the cellular dynamics of DrSSB in response to DNA damage.

Main Methods:

• X-ray crystallography to determine the structure of the DrSSB-ssDNA complex.
• Electron microscopy to observe ssDNA-binding modes.
• In vivo studies to track DrSSB cellular dynamics post-irradiation.

Main Results:

• The crystal structure revealed ssDNA binding surfaces analogous to homotetrameric SSBs, with unique contacts for species-specific binding.
• Electron microscopy showed two salt-dependent ssDNA-binding modes, similar to E. coli SSB.
• In vivo, DrSSB levels significantly increased after ionizing radiation exposure, forming a transient nucleoid-centric focus that dispersed over time.

Conclusions:

• DrSSB's structure, while unusual, shares functional similarities with other bacterial SSBs.
• DrSSB exhibits dynamic cellular behavior following radiation exposure, potentially organizing DNA repair processes.
• These findings suggest DrSSB plays a critical role in the remarkable radiation resistance of Deinococcus radiodurans.