Filamentous bacteriophage coat protein undergoes a remarkable structural transition during the viral assembly process as it is transferred from the membrane environment of the cell, where it spans the phospholipid bilayer, to the newly extruded virus particles. Nuclear magnetic resonance (NMR) studies show the membrane-bound form of the 46-residue Pf1 coat protein to be surprisingly complex with five distinct regions. The secondary structure consists of a long hydrophobic helix (residues 19 to 42) that spans the bilayer and a short amphipathic helix (residues 6 to 13) parallel to the plane of the bilayer. The NH2-terminus (residues 1 to 5), the COOH-terminus (residues 43 to 46), and residues 14 to 18 connecting the two helices are mobile. By comparing the structure and dynamics of the membrane-bound coat protein with that of the viral form as determined by NMR and neutron diffraction, essential features of assembly process can be identified.

The colicin E1 channel polypeptide was shown to be organized anisotropically in membranes by solid-state NMR analysis of samples of uniformly 15N-labeled protein in oriented planar phospholipid bilayers. The 190 residue C-terminal colicin E1 channel domain is the largest polypeptide to have been characterized by 15N solid-state NMR spectroscopy in oriented membrane bilayers. The 15N-NMR spectra of the colicin E1 show that: (1) the structure and dynamics are independent of anionic lipid content in both oriented and unoriented samples; (2) assuming the secondary structure of the polypeptide is helical, there are both trans-membrane and in-plane helical segments; (3) trans-membrane helices account for approximately 20-25% of the channel polypeptide, which is equivalent to 38-48 residues of the 190-residue polypeptide. The results of the two-dimensional PISEMA spectrum are interpreted in terms of a single trans-membrane helical hairpin inserted into the bilayer from each channel molecule. These data are also consistent with this helical hairpin being derived from the 38-residue hydrophobic segment near the C-terminus of the colicin E1 channel polypeptide.

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