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The replication machinery encoded by SCCmec and related mobile genetic elements
Author(s) -
Rice Phoebe A,
MirSanchis Ignacio,
BoyleVavra Susan,
Pigli Ying Zhang
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.389.3
Subject(s) - recombinase , biology , genetics , mobile genetic elements , helicase , gene , sccmec , horizontal gene transfer , dna repair , insertion sequence , dna , genome , transposable element , rna , recombination , bacteria , staphylococcus aureus , methicillin resistant staphylococcus aureus
SCCs are a family of mobile genomic islands, that, when carrying methicillin resistance in S. aureus , create MRSA strains. Our combined bioinformatics, biochemical and structural work strongly implies that SCC elements can replicate after excision, which has not been previously suggested, but which would increase the efficiency of any horizontal gene transfer mechanism. We began with a bio‐informatic approach. Although the recombinases responsible for excision and insertion of these elements have been identified, nothing else is known about their genetic machinery. We compared a broad range of SCC element sequences to determine what additional genes (and functions) are conserved, and unexpectedly found putative DNA replication machinery: the recombinases are flanked on one side by a uracil DNA glycosylase inhibitor, and on the other by a large putative ATPase. Two different types of ATPase were found, but both have homologs among the self‐loading helicases that initiate replication of the otherwise‐unrelated staphylococcal pathogenicity islands (SaPIs). Furthermore, we found that the staphylococcal SCC elements are part of a broader family of mobile genetic elements that infest gram‐positive bacteria. These elements have similar recombinase genes that are preceded by putative replication initiators, and are always found inserted into the same chromosomal site (the 3′ end of a putative ribosomal pseudo‐U methyltransferase gene). We began our functional investigation of this machinery with the ATPase from SCCmec type IV, termed Cch. We have shown that Cch is a functional helicase with 3′ to 5′ polarity, and that it binds dsDNA with weak sequence specificity for the intergenic region following its own coding frame, which is where the origin is found for the related SaPI Rep proteins. We also determined the crystal structure of Cch in complex with AMPPNP. It forms a hexameric ring with a positively charge central pore. The N‐terminal domain appears to have a unique fold, the C‐terminal domain forms a winged helix‐turn‐helix that binds dsDNA, and the central AAA ATPase domain has an unusual arrangement of subdomains that, among DNA‐binding ATPases, is only shared by the archaeal and eukaryotic MCM helicases. Support or Funding Information R21 AI117593‐01Cch hexamer, shaded from blue (N) to red (C).