Recombinant Photorhabdus luminescens subsp. laumondii DNA repair protein recO (recO)
Description
Molecular Structure and Biochemical Properties
RecO proteins are evolutionarily conserved recombination mediator proteins (RMPs) that share structural and functional similarities with eukaryotic Rad52. In P. luminescens, RecO is predicted to contain:
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DNA-binding domains: Enable interaction with single-stranded DNA (ssDNA) and displacement of single-stranded DNA-binding proteins (SSBs).
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RecR interaction motifs: Critical for forming RecO–RecR complexes, which regulate RecO’s activity during recombination.
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Zinc-binding sites: In some bacterial RecO homologs (e.g., Mycobacterium smegmatis), zinc modulates DNA-binding affinity during strand annealing .
Functional Role in DNA Repair
RecO primarily functions in two processes:
Strand Annealing and Recombination Initiation
RecO catalyzes the annealing of complementary ssDNA regions, bypassing the need for extensive homology search. This is critical for repairing DSBs and restarting stalled replication forks. In E. coli, RecO mediates the annealing of SSB-coated ssDNA, a reaction inhibited by RecR at high concentrations . In P. luminescens, similar mechanisms are likely conserved, though specific interactions with SSB or RecR remain uncharacterized.
RecA Loading and Recombination
RecO facilitates the displacement of SSB proteins and loads RecA onto ssDNA to form nucleoprotein filaments, which drive HR. This process is regulated by RecR, which modulates RecO’s activity . In E. coli, RecO–RecR complexes enhance RecA strand invasion, a function that may extend to P. luminescens .
Interactions with Other DNA Repair Proteins
RecO’s activity is tightly regulated by interactions with:
a. Homologous Recombination in P. luminescens
While direct studies on P. luminescens RecO are absent, insights from related systems highlight its potential role:
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Recombineering: In P. luminescens, Pluγ (a RecBCD inhibitor) enhances homologous recombination efficiency, suggesting interplay between RecFOR and RecBCD pathways . RecO may compensate for RecBCD activity in HR.
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Stress Response: RecO’s role in repairing replication fork collapse is critical for bacterial survival under genotoxic stress.
Mechanistic Insights from Model Organisms
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Zinc-Dependent Annealing: In M. smegmatis, zinc stimulates RecO’s ssDNA-binding, enabling annealing without RecR . This contrasts with E. coli, where RecR regulates annealing . P. luminescens RecO’s zinc dependency remains unexplored.
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Species-Specific SSB Interactions: E. coli RecO requires its cognate SSB for optimal annealing, while M. smegmatis RecO does not . P. luminescens SSB interactions are hypothetical.
Applications and Future Directions
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Biotechnology: RecO’s role in HR makes it a candidate for enhancing genetic engineering in P. luminescens, a symbiont of entomopathogenic nematodes.
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Antibiotic Resistance: Targeting RecO could disrupt bacterial DNA repair pathways, offering novel therapeutic strategies.
Product Specs
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Target Background
KEGG: plu:plu3338
STRING: 243265.plu3338
Q&A
Basic Research Questions
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What is the biological role of RecO in Photorhabdus luminescens?
RecO functions as a key DNA repair protein in P. luminescens, playing an essential role in homologous recombination pathways. Based on studies of RecO homologs in other bacterial species, this protein likely operates within the RecFOR pathway to facilitate DNA damage repair, particularly at stalled replication forks. The RecO protein has the ability to displace single-stranded binding proteins (SSB) and facilitate the production of RecA-coated ssDNA filaments, which are crucial for homologous recombination processes . This function is particularly important for P. luminescens during its complex lifecycle transitions between insect host, nematode partner, and soil environments, where it encounters various DNA-damaging stressors.
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What structural features characterize P. luminescens RecO protein?
While the specific structure of P. luminescens RecO has not been directly determined in the available studies, structural insights can be inferred from homologous proteins such as Deinococcus radiodurans RecO (drRecO). The RecO protein typically contains three discrete structural regions: an N-terminal oligonucleotide/oligosaccharide-binding domain, a central helical bundle, and a C-terminal zinc-finger motif . These structural elements provide multiple binding sites for interaction with both DNA substrates and other proteins in the DNA repair pathway. The ability to bind both single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA), potentially simultaneously at different binding sites, reflects RecO's central role in DNA repair at replication forks.
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How does RecO interact with DNA during repair processes?
RecO demonstrates versatile DNA-binding capabilities that are fundamental to its repair functions. Studies with homologous RecO proteins show that it can bind both ssDNA and dsDNA, with these interactions potentially occurring simultaneously on different DNA-binding sites of the protein . The binding involves interaction between positively charged residues on RecO and the negatively charged phosphate backbone of DNA. This non-sequence-specific interaction with the DNA backbone allows RecO to function in diverse DNA repair scenarios. The DNA-binding properties of RecO can be modulated by the presence of divalent cations such as Mg²⁺, which affects the strength and nature of protein-DNA interactions . This versatile DNA binding capacity is essential for RecO's role in facilitating homologous recombination at sites of DNA damage.
