Colicin B consists of a single polypeptide chain

Braun, Volkmar; Maas, Edith

doi:10.1111/j.1574-6968.1984.tb00192.x

Cited by 7 publications

(1 citation statement)

References 10 publications

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“…Furthermore, the acidic molten globule state of colicin A is also of great biological interest since it has a clear functional role. Colicins A and B ( − ) are the only two colicins which form this structure at low pH. The remaining colicin pore-forming domains show either limited pH sensitivity, like colE1-P (), or none at all, like colN-P().…”

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confidence: 99%

Surface Aspartate Residues Are Essential for the Stability of Colicin A P-Domain: A Mechanism for the Formation of an Acidic Molten-Globule^,

Fridd

Lakey

2002

Biochemistry

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The pore-forming domains of members of a family of bacterial toxins, colicins N and A, share > 50% sequence identity, identical folds and yet display strikingly different behavior in acid conditions. At low pH colicin A forms a molten globule state while colicin N retains a native fold. This is relevant to in vivo activity since colicin A requires acidic phospholipids for its toxic activity but colicin N does not. The pI of colicin A (5.25) is far lower than that of colicin N (10.2) because colicin A contains seven extra aspartate residues. We first introduced separately each of these acidic amino acids into homologous sites in colicin N, but none caused destabilization at low pH. However, in the reverse experiment, the sequential replacement of these acidic side chains of colicin A by alanine revealed six sites where this change destabilized the protein at neutral pH. Some of these residues, which each contribute less than 4% to the total negative charge, appear to stabilize the protein via a network of hydrogen bonds and charge pairs which are sensitive to protonation. Other residues have no clear interactions that explain their importance. The colicin A is thus a protein that relies upon acid sensitive interactions for its stability at neutral pH and its in vivo activity.

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Surface Aspartate Residues Are Essential for the Stability of Colicin A P-Domain: A Mechanism for the Formation of an Acidic Molten-Globule^,

Fridd

Lakey

2002

Biochemistry

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Prozess des Risikomanagements

Risikomanagement- Und Überwachungssystem Nach KonTraG

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Formation of ion channels by Colicin B in planar lipid bilayers

et al. 1990

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The gene for the antibacterial peptide colicin B was cloned and transformed into a host background where it was constitutively overexpressed. The purified gene product was biologically active and formed voltage-dependent, ion-conducting channels in planar phospholipid bilayers composed of asolectin. Colicin B channels exhibited two distinct unitary conductance levels, and a slight preference for Na+ over Cl-. Kinetic analysis of the voltage-driven opening and closing of colicin channels revealed the existence of at least two conducting states and two nonconducting states of the protein. Both the ion selectivity and the kinetics of colicin B channels were highly dependent on pH. Excess colicin protein was readily removed from the system by perfusing the bilayer, but open channels could be washed out only after they were allowed to close. A monospecific polyclonal antiserum generated against electrophoretically purified colicin B eliminated both the biological and in vitro activity of the protein. Membrane-associated channels, whether open or closed, remained functionally unaffected by the presence of the antiserum. Taken together, our results suggest that the voltage-independent binding of colicin B to the membrane is the rate-limiting step for the formation of ion channels, and that this process is accompanied by a major conformational rearrangement of the protein.

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Colicin B consists of a single polypeptide chain

Abstract: Colicin B was isolated in pure form from Escherichia coli Cl139 and was shown to consist of a single polypeptide chain with an apparent Mr of 70000. Therefore, it does not differ from other colicins where the toxic activity resides in one polypeptide.

Cited by 7 publications

References 10 publications

Surface Aspartate Residues Are Essential for the Stability of Colicin A P-Domain: A Mechanism for the Formation of an Acidic Molten-Globule^,

Surface Aspartate Residues Are Essential for the Stability of Colicin A P-Domain: A Mechanism for the Formation of an Acidic Molten-Globule^,

Prozess des Risikomanagements

Formation of ion channels by Colicin B in planar lipid bilayers

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Colicin B consists of a single polypeptide chain

Abstract: Colicin B was isolated in pure form from Escherichia coli Cl139 and was shown to consist of a single polypeptide chain with an apparent Mr of 70000. Therefore, it does not differ from other colicins where the toxic activity resides in one polypeptide.

Cited by 7 publications

References 10 publications

Surface Aspartate Residues Are Essential for the Stability of Colicin A P-Domain: A Mechanism for the Formation of an Acidic Molten-Globule,

Surface Aspartate Residues Are Essential for the Stability of Colicin A P-Domain: A Mechanism for the Formation of an Acidic Molten-Globule,

Prozess des Risikomanagements

Formation of ion channels by Colicin B in planar lipid bilayers

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Surface Aspartate Residues Are Essential for the Stability of Colicin A P-Domain: A Mechanism for the Formation of an Acidic Molten-Globule^,

Surface Aspartate Residues Are Essential for the Stability of Colicin A P-Domain: A Mechanism for the Formation of an Acidic Molten-Globule^,