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Contributions of F‐specific subunits to the F plasmid‐encoded type IV secretion system and F pilus
Author(s) -
Kishida Kouhei,
Bosserman Rachel E.,
Harb Laith,
Khara Pratick,
Song Liqiang,
Hu Bo,
Zeng Lanying,
Christie Peter J.
Publication year - 2022
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.14908
Subject(s) - pilus , plasmid , biology , mutant , bacterial conjugation , secretion , protein subunit , microbiology and biotechnology , gene , horizontal gene transfer , escherichia coli , phenotype , enterobacteriaceae , genetics , biochemistry , phylogenetics
Abstract F plasmids circulate widely among the Enterobacteriaceae through encoded type IV secretion systems (T4SS F s). Assembly of T4SS F s and associated F pili requires 10 VirB/VirD4‐like Tra subunits and eight or more F‐specific subunits. Recently, we presented evidence using in situ cryoelectron tomography (cryoET) that T4SS F s undergo structural transitions when activated for pilus production, and that assembled pili are deposited onto alternative basal platforms at the cell surface. Here, we deleted eight conserved F‐specific genes from the MOBF12C plasmid pED208 and quantitated effects on plasmid transfer, pilus production by fluorescence microscopy, and elaboration of T4SS F structures by in situ cryoET. Mutant phenotypes supported the assignment of F‐specific subunits into three functional Classes: (i) TraF, TraH, and TraW are required for all T4SS F ‐associated activities, (ii) TraU, TraN, and TrbC are nonessential but contribute significantly to distinct T4SS F functions, and (iii) TrbB is essential for F pilus production but not for plasmid transfer. Equivalent mutations in a phylogenetically distantly related MOB12A F plasmid conferred similar phenotypes and generally supported these Class assignments. We present a new structure‐driven model in which F‐specific subunits contribute to distinct steps of T4SS F assembly or activation to regulate DNA transfer and F pilus dynamics and deposition onto alternative platforms.