![]() The three-dimensional structure of the membrane-bound form of fd coat protein, which has been determined in micelles by solution NMR ( 11), and in bilayers by solid-state NMR ( 12), is that of a typical membrane protein with a hydrophobic transmembrane helix connected by a short loop to an amphipathic in-plane helix that interacts with the lipid head groups. Filamentous bacteriophage coat proteins are popular systems for the development of NMR methods applicable to helical membrane proteins in micelles ( 5– 10). Although filamentous bacteriophages do not have a membrane, the major coat protein (pVIII) is a membrane protein in the course of the viral lifecycle because it is stored in the bacterial membrane after synthesis and processing before the assembly of new virus particles. fd, M13, and f1 are very similar inoviruses with their single-stranded circular DNA packaged inside a cylinder that consists almost entirely of ≈2,700 copies of structurally identical coat protein subunits. New NMR results include the complete sequential assignment of the two-dimensional polarization inversion spin-exchange at the magic angle spectrum of a uniformly 15N-labeled 50-residue protein in a 1.6 × 10 7 Da particle in solution, and the calculation of the three-dimensional structure of the protein from orientational restraints with an accuracy equivalent to an rms deviation of ≈1Å.įilamentous bacteriophages have been studied in the context of a wide range of prokaryotic biology ( 1, 2, 3), and they have essential roles in many laboratory procedures of molecular biology and biotechnology, including the cloning and sequencing of DNA, and the generation and screening of peptide libraries ( 1, 4). In addition to their roles in molecular biology and biotechnology, the filamentous bacteriophages continue to serve as model systems for the development of experimental methods for determining the structures of proteins in biological supramolecular assemblies. The structure of the coat protein in virus particles, in combination with the structure of the membrane-bound form of the same protein in bilayers, also recently determined by solid-state NMR spectroscopy, provides insight into the viral assembly process. Residues 1–5 have been shown to be mobile and unstructured, and proline 6 terminates the helix. Most notably, the 50-residue protein is not a single curved helix, but rather is a nearly ideal straight helix between residues 7 and 38, where there is a distinct kink, and then a straight helix with a different orientation between residues 39 and 49. The atomic resolution structure of fd coat protein determined by solid-state NMR spectroscopy of magnetically aligned filamentous bacteriophage particles differs from that previously determined by x-ray fiber diffraction.
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