Tilted, extended, and lying in wait: the membrane-bound topology of residues Lys-381-Ser-405 of the colicin E1 channel domain.
The membrane-bound closed state (zero potential) of the helix 3 segment (Lys-381-Ser-405) of the colicin E1 channel domain was investigated by site-directed fluorescence labeling using a bimane probe tethered to a single cysteine residue of each mutant protein. A number of fluorescence properties of the tethered bimane probe were measured for the soluble channel mutant proteins as well as for the membrane-bound proteins. A new method called helical periodicity surface analysis was employed to fit the fluorescence data to a harmonic wave function using four different statistical methods. The fit of the various data sets to a harmonic wave function indicated that the periodicity of helix 3 in the membrane-bound state is typical for an amphipathic alpha helix (3.7-4.0 residues per turn and an angular frequency between 90 and 97 degrees). Notably, upon membrane binding, helix 3 elongates from 15 residues (soluble structure) to 20 residues by a three- and two-residue extension at the N- and C-termini of the helix, respectively. Dual quencher analysis also revealed that helix 3 is appressed to the surface of the membrane with its N-terminus more deeply buried within the interfacial region of the bilayer than its C-terminus. Finally, contrary to a previous report, our data show that helices 3 and 4 remain separate and independent helices upon membrane association in the absence of a membrane potential.
Wei
Zhikui
Z
Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada N1G 2W1.
White
Dawn
D
Wang
Jie
J
Musse
Abdiwahab A
AA
Merrill
A Rod
AR
D000595:Amino Acid Sequence; D003087:Colicins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008239:Lysine / Q000235:genetics; D008564:Membrane Potentials; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D012694:Serine / Q000235:genetics
D003087:Colicins; D029968:Escherichia coli Proteins; C488857:Imm protein, E coli; D008051:Lipid Bilayers; D010446:Peptide Fragments; D012694:Serine; D008239:Lysine