6hn7
From Proteopedia
Hijacking the Hijackers: Escherichia coli Pathogenicity Islands Redirect Helper Phage Packaging for Their Own Benefit.
Structural highlights
Function[TERS_LAMBD] Component of the terminase that processes and encapsidates viral genomes during virion assembly. The terminase is composed of two small and one large subunits. To initiate packaging, it binds a specific sequence called cos, at the junction of adjacent viral genomes in the concatemeric DNA substrate. Next, in a reaction stimulated by the presence of proheads and ATP but not requiring ATP hydrolysis, the terminase creates two nicks 12bp appart at the cos site, one on each stand. Terminase then separates the cohesive ends in a reaction requiring ATP hydrolysis. The heterotrimer remains bound to the left end of the genome to be packaged, forming a stable DNA-protein complex known as complex I. In a reaction facilitated by a viral assembly catalyst, gpFI, complex I binds a prohead, a preformed head shell precursor, to form complex II. In another packaging reaction requiring ATP hydrolysis, the DNA is translocated into the prohead until the next cos site on the concatemer reaches the packaging complex. At this time the downstream cos site is cut and the heterotrimer undocks from the DNA-filled head to remain bound to the left end of concatemer's next genome. The new heterotrimer-DNA complex I binds another prohead to continue the processive, polarized packaging of viral genomes. The terminase is dependent upon host integration host factor (ihfA/ihfB) for these activities.[1] Publication Abstract from PubMedPhage-inducible chromosomal islands (PICIs) represent a novel and universal class of mobile genetic elements, which have broad impact on bacterial virulence. In spite of their relevance, how the Gram-negative PICIs hijack the phage machinery for their own specific packaging and how they block phage reproduction remains to be determined. Using genetic and structural analyses, we solve the mystery here by showing that the Gram-negative PICIs encode a protein that simultaneously performs these processes. This protein, which we have named Rpp (for redirecting phage packaging), interacts with the phage terminase small subunit, forming a heterocomplex. This complex is unable to recognize the phage DNA, blocking phage packaging, but specifically binds to the PICI genome, promoting PICI packaging. Our studies reveal the mechanism of action that allows PICI dissemination in nature, introducing a new paradigm in the understanding of the biology of pathogenicity islands and therefore of bacterial pathogen evolution. Hijacking the Hijackers: Escherichia coli Pathogenicity Islands Redirect Helper Phage Packaging for Their Own Benefit.,Fillol-Salom A, Bacarizo J, Alqasmi M, Ciges-Tomas JR, Martinez-Rubio R, Roszak AW, Cogdell RJ, Chen J, Marina A, Penades JR Mol Cell. 2019 Jul 8. pii: S1097-2765(19)30473-3. doi:, 10.1016/j.molcel.2019.06.017. PMID:31350119[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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