Gating movements of colicin A and colicin Ia are different.
Both colicin A and colicin Ia belong to a subfamily of the bacterial colicins that act by forming a voltage-dependent channel in the inner membrane of target bacteria. Both colicin A and Ia open at positive and close at negative potential, but only colicin A exhibits distinctly biphasic turnoff kinetics, implying the existence of two open states. Previous work has shown that Colicin Ia gating is associated with the translocation of a region representing 4 of its alpha helices across the membrane. Also, if its C-terminal, channel-forming domain is detached from the other domains, its N-terminal alpha helix can now also cross the membrane, causing the conductance to drop by a factor of about 6. Colicin A gating also involves the translocation of an internal domain, but we find that its translocated domain is somewhat smaller than that of Ia. Furthermore, while its isolated C-terminal domain can also undergo a transition to a smaller conductance, the conductance change is only about 15%, and the transition does not involve the translocation of the N-terminal alpha helix. Trapping the N-terminus on the cis side prevents neither this small conductance transition nor the biphasic turn-off. So, while the gating of both channels involves large, currently inexplicable conformational changes, these motions are qualitatively different in the two proteins, which may be a reflection of the dissimilar kinetics of closing.
Slatin
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SL
Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, NY 10461, USA. slatin@aecom.yu.edu
Duché
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D
Kienker
P K
PK
Baty
D
D
D000595:Amino Acid Sequence; D003087:Colicins / Q000737:chemistry* / Q000378:metabolism*; D007202:Indicators and Reagents / Q000494:pharmacology; D015640:Ion Channel Gating / Q000502:physiology*; D007473:Ion Channels / Q000737:chemistry / Q000502:physiology*; D008051:Lipid Bilayers; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000187:drug effects / Q000235:genetics; D011487:Protein Conformation; D021381:Protein Transport; D017386:Sequence Homology, Amino Acid; D019809:Streptavidin / Q000494:pharmacology; D013329:Structure-Activity Relationship
D003087:Colicins; D007202:Indicators and Reagents; D007473:Ion Channels; D008051:Lipid Bilayers; D019809:Streptavidin