Resolving the 3D spatial orientation of helix I in the closed state of the colicin E1 channel domain by FRET. Insights into the integration mechanism.
Current evidence suggests that the closed-state membrane model for the channel-forming domain of colicin E1 involves eight amphipathic α-helices (helices I-VII and X) that adopt a two-dimensional arrangement on the membrane surface. Two central hydrophobic α-helices in colicin E1 (VIII and IX) adopt a transmembrane location-the umbrella model. Helices I and II have been shown to participate in the channel by forming a transmembrane segment (TM1) in the voltage-induced open channel state. Consequently, it is paramount to determine the relative location and orientation of helix I in the two-dimensional arrangement of the membrane. A new, low-resolution, three-dimensional model of the closed state of the colicin E1 channel was constructed based on FRET measurements between three naturally occurring Trp residues and three sites in helix I, in addition to previously reported FRET distances for the channel domain. Furthermore, a new mechanism for the channel integration process involving the transition of the soluble to membrane-bound form is presented based on a plethora of kinetic data for this process.
Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada.
Miguel R
MR
Lugo
Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada.
Derek
D
Ho
Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada. Electronic address: rmerrill@uoguelph.ca.
A Rod
AR
Merrill
D016880:Anisotropy; D001643:Bridged Bicyclo Compounds / Q000737:chemistry; D002462:Cell Membrane / Q000737:chemistry; D003087:Colicins / Q000737:chemistry*; D003545:Cysteine / Q000737:chemistry; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D031541:Fluorescence Resonance Energy Transfer; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D000072417:Protein Domains; D017433:Protein Structure, Secondary; D014364:Tryptophan / Q000737:chemistry
D001643:Bridged Bicyclo Compounds; D003087:Colicins; D029968:Escherichia coli Proteins; D014364:Tryptophan; D003545:Cysteine; C028381:monobromobimane
Colicin E1; FRET; Ion channels; Lifetime fluorescence; Molecular modeling