8txr | pdb_00008txr
E. coli ExoVII(H238A)
Structural highlights
FunctionEX7L_ECOLI Bidirectionally degrades single-stranded DNA into large acid-insoluble oligonucleotides, which are then degraded further into small acid-soluble oligonucleotides. It can degrade 3' or 5' ss regions extending from the termini of duplex DNA molecules and displaced ss regions. It can also excise thymine dimers in vitro (Probable) (PubMed:22718974, PubMed:4602029, PubMed:4602030). ssDNA-binding requires both subunits (PubMed:22718974). Required for production of the mature 5'-end of retron Ec78 or Ec83 msDNA. Overproduction of this subunit in the absence of an equivalent quantity of the small subunit is toxic, causing cell elongation and chromosome fragmentation or loss; its toxicity is mostly suppressed by RecA (PubMed:26626352).[1] [2] [3] [4] [5] Publication Abstract from PubMedExonuclease VII (ExoVII) is a ubiquitous bacterial nuclease. Encoded by the xseA and xseB genes, ExoVII participates in multiple nucleic acid-dependent pathways including the processing of multicopy single-stranded DNA and the repair of covalent DNA-protein crosslinks (DPCs). Although many biochemical properties of ExoVII have been defined, little is known about its structure/function relationships. Here, we use cryoelectron microscopy (cryoEM) to determine that Escherichia coli ExoVII comprises a highly elongated XseA(4).XseB(24) holo-complex. Each XseA subunit dimerizes through a central extended alpha-helical segment decorated by six XseB subunits and a C-terminal, domain-swapped beta-barrel element; two XseA(2).XseB(12) subcomplexes further associate using N-terminal OB (oligonucleotide/oligosaccharide-binding) folds and catalytic domains to form a spindle-shaped, catenated octaicosamer. The catalytic domains of XseA, which adopt a nuclease fold related to 3-dehydroquinate dehydratases, are sequestered in the center of the complex and accessible only through large pores formed between XseA tetramers. The architectural organization of ExoVII, combined with biochemical studies, indicate that substrate selectivity is controlled by steric access to its nuclease elements and that tetramer dissociation results from substrate DNA binding. Despite a lack of sequence and fold homology, the physical organization of ExoVII is reminiscent of Mre11.Rad50/SbcCD ATP (adenosine triphosphate)-dependent nucleases used in the repair of double-stranded DNA breaks, including those formed by DPCs through aberrant topoisomerase activity, suggesting that there may have been convergent evolutionary pressure to contend with such damage events. Structure of Escherichia coli exonuclease VII.,Liu C, Hauk G, Yan Q, Berger JM Proc Natl Acad Sci U S A. 2024 Jan 30;121(5):e2319644121. doi: , 10.1073/pnas.2319644121. Epub 2024 Jan 25. PMID:38271335[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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