Membrane-bound state of the colicin E1 channel domain as an extended two-dimensional helical array

S. D. Zakharov, M. Lindeberg, Y. Griko, Z. Salamon, G. Tollin, F. G. Prendergast, W. A. Cramer

Research output: Contribution to journalArticle

74 Scopus citations

Abstract

Atomic level structures have been determined for the soluble forms of several colicins and toxins, but the structural changes that occur after membrane binding have not been well characterized. Changes occurring in the transition from the soluble to membrane-bound state of the C-terminal 190- residue channel polypeptide of colicin E1 (P190) bound to anionic membranes are described. In the membrane-bound state, the α-helical content increases from 60-64% to 80-90%, with a concomitant increase in the average length of the helical segments from 12 to 16 or 17 residues, close to the length required to span the membrane bilayer in the open channel state. The average distant between helical segments is increased and interhelix interactions are weakened, as shown by a major loss of tertiary structure interactions, decreased efficiency of fluorescence resonance energy transfer from an energy donor on helix V of P190 to an acceptor of helix IX, and decreased resonance energy transfer at higher temperatures, not observed in soluble P190, implying freedom of motion of helical segments. Weaker interactions are also shown by a calorimetric thermal transition of low cooperativity, and the extended nature of the helical array is shown by a 3- to 4-fold increase in the average area subtended per molecule to 4,200 Å2 on the membrane surface. The latter, with analysis of the heat capacity changes, implies the absence of a developed hydrophobic core in the membrane-bound P190. The membrane interfacial layer thus serves to promote formation of a highly helical extended two-dimensional flexible net. The properties of the membrane-bound state of the colicin channel domain (i.e., hydrophobic anchor, lengthened and loosely coupled α-helices, and close association with the membrane interfacial layer) are plausible structural features for the state that is a prerequisite for voltage gating, formation of transmembrane helices, and channel operating.

Original languageEnglish (US)
Pages (from-to)4282-4287
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume95
Issue number8
DOIs
StatePublished - Apr 14 1998

Keywords

  • Amphipathic helix
  • Apoptosis
  • Diptheria toxin
  • Membrane interfacial layer
  • Molten globule

ASJC Scopus subject areas

  • General

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