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Transport of proteins across membranes: structure of the colicin I receptor bound to colicin Ia
Author(s) -
Buchanan Susan K.,
Lukacik Petra,
Grizot Sylvestre,
Ghirlando Rodolfo,
Ali Maruf M.U.,
Barnard Travis J.,
Jakes Karen S.,
Kienker Paul K.,
Esser Lothar
Publication year - 2007
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.21.5.a148-c
Subject(s) - colicin , bacterial outer membrane , periplasmic space , biophysics , biology , inner membrane , receptor , cell membrane , lipid bilayer , microbiology and biotechnology , chemistry , biochemistry , escherichia coli , membrane , gene
Colicin Ia kills susceptible E. coli cells by binding to a specific receptor in the outer membrane, colicin I receptor, and subsequently translocating its channel forming domain across the periplasmic space. Upon making contact with the inner membrane, the channel forming domain spontaneously inserts into the lipid bilayer and forms a voltage‐dependent ion channel, which causes cell death. We determined crystal structures of colicin I receptor, which is a TonB dependent (small molecule) transporter, alone and in complex with the receptor binding domain of colicin Ia. The binding of colicin Ia stabilizes an altered conformational state of the receptor, where two extracellular loops undergo a large, concerted movement to open outwards, exposing the interior of the barrel to the environment and to the colicin. In vivo killing assays using full‐length colicin Ia show that colicin I receptor is necessary for cell susceptibility, and that the receptor likely transports colicin Ia across the outer membrane without help from other outer membrane proteins. TonB box mutations in either Cir or colicin Ia prevent killing, implying that two interactions with TonB protein are required for colicin translocation. Our data suggest that colicin Ia actively participates in translocation of colicin Ia. The differences between small molecule and large protein translocation by the same transporters will be discussed.