Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2010 Sep 8;99(5):1465-74.
doi: 10.1016/j.bpj.2010.06.009.

Structure and Dynamics of the Membrane-Bound Form of Pf1 Coat Protein: Implications of Structural Rearrangement for Virus Assembly

Affiliations
Free PMC article

Structure and Dynamics of the Membrane-Bound Form of Pf1 Coat Protein: Implications of Structural Rearrangement for Virus Assembly

Sang Ho Park et al. Biophys J. .
Free PMC article

Abstract

The three-dimensional structure of the membrane-bound form of the major coat protein of Pf1 bacteriophage was determined in phospholipid bilayers using orientation restraints derived from both solid-state and solution NMR experiments. In contrast to previous structures determined solely in detergent micelles, the structure in bilayers contains information about the spatial arrangement of the protein within the membrane, and thus provides insights to the bacteriophage assembly process from membrane-inserted to bacteriophage-associated protein. Comparisons between the membrane-bound form of the coat protein and the previously determined structural form found in filamentous bacteriophage particles demonstrate that it undergoes a significant structural rearrangement during the membrane-mediated virus assembly process. The rotation of the transmembrane helix (Q16-A46) around its long axis changes dramatically (by 160 degrees) to obtain the proper alignment for packing in the virus particles. Furthermore, the N-terminal amphipathic helix (V2-G17) tilts away from the membrane surface and becomes parallel with the transmembrane helix to form one nearly continuous long helix. The spectra obtained in glass-aligned planar lipid bilayers, magnetically aligned lipid bilayers (bicelles), and isotropic lipid bicelles reflect the effects of backbone motions and enable the backbone dynamics of the N-terminal helix to be characterized. Only resonances from the mobile N-terminal helix and the C-terminus (A46) are observed in the solution NMR spectra of the protein in isotropic q > 1 bicelles, whereas only resonances from the immobile transmembrane helix are observed in the solid-state (1)H/(15)N-separated local field spectra in magnetically aligned bicelles. The N-terminal helix and the hinge that connects it to the transmembrane helix are significantly more dynamic than the rest of the protein, thus facilitating structural rearrangement during bacteriophage assembly.

Figures

Figure 1
Figure 1
2D solid-state NMR 1H/15N SLF spectra of uniformly and selectively 15N-labeled (by residue type) samples of the membrane-bound form of Pf1 coat protein in 14-O-PC/6-O-PC (q = 3.2) bilayers aligned with their normal perpendicular to the magnetic field. The PISA wheel (thin line) for an ideal α-helix with uniform dihedral angles (ϕ = −61°, φ = −45°), tilted 30° from the membrane normal, is superimposed on the experimental spectra. The residue number designates the resonance assignments for each type of labeled amino acid. (A) The data from uniformly 15N-labeled coat protein were described previously (6), and are provided for comparison to the spectra of the selectively labeled samples in (B-F). (B) 15N -valine labeled. (C) 15N-leucine labeled. (D) 15N-isoleucine labeled. (E) 15N-alanine labeled. (F) 15N -lysine labeled.
Figure 2
Figure 2
3D structures of the Pf1 coat protein. (A and B) The membrane-bound form of the protein (PDB: 2KSJ). (C and D) The structural form in the intact bacteriophage particle (PDB: 1PJF). The axis of alignment (z) is parallel to the magnetic field and the membrane normal in A and B, and to the long axis of Pf1 bacteriophage in C and D. In the membrane-bound form of the protein, the acidic N-terminus region is exposed to the bacterial periplasmic space (peri) and the basic C-terminal region is exposed to the cytoplasm (cyto). Acidic residues (Asp and Glu) are shown in red, conserved glycine residues in the transmembrane helix are in yellow, basic residues (Arg and Lys) are in blue, and interfacial tyrosines are in pink. Residues R44 and K45 face the cytoplasm in the membrane-bound form and the DNA on the interior of the bacteriophage particles. (B and D) Images obtained by 90° rotation of A and C around the z axis of the images shown in A and C, respectively.
Figure 3
Figure 3
Summary of the experimental data used to characterize the secondary structure and backbone dynamics of the membrane-bound form of Pf1 coat protein in DHPC micelles by solution NMR. The measurements are plotted as a function of residue number for the protein sequence aligned at the top of the figure. Above the sequence is a schematic drawing of the secondary structure; the light gray region is the amphipathic N-terminal helix and the dark gray region is the hydrophobic trans-membrane helix. (A and B) Dipolar waves fit to 1H-15N RDCs. (A) Sample weakly aligned in a stressed polyacrylamide gel. (B) Sample weakly aligned by the presence of fd bacteriophages in the solution (16). (C) 1H/15N heteronuclear NOEs. (DG). Normalized peak intensities of the amide resonances observed in 2D 1H/15N HSQC spectra samples with different q values for the ratio of DMPC (long chain lipid) to DHPC (short chain lipid) in isotropic bicelles. (D) q = 0. (E) q = 0.25. (F) q = 0.5. (G) q = 1.
Figure 4
Figure 4
1D solid-state 15N NMR spectra of the membrane-bound form of Pf1 coat protein in lipid bilayers aligned with their normals parallel to the magnetic field. (A–C) DOPC/DOPG (9/1, w/w) planar lipid bilayers mechanically aligned on glass slides. (D–F) 14-O-PC/6-O-PC (q = 3.2) bilayers magnetically by addition of YbCl3. (A and D) Uniformly 15N-labeled. (BF) Selectively 15N-labeled (by residue type). (B and E) 15N-isoleucine labeled. (C and F) 15N-threonine labeled. Signals from residues in the amphipathic N-terminal region (I12, T5 and T13) are present in the spectra from samples mechanically-aligned on glass plates (B and C), but are not observed in the spectra from magnetically-aligned samples (E and F). In contrast, signals from the trans-membrane region (I22, I26, I32 and I39) are present in the spectra from both mechanically- and magnetically-aligned samples. The data from the magnetically-aligned sample of the uniformly 15N-labeled protein were described previously (6), and provide for comparison to the spectra of the selectively labeled samples.
Figure 5
Figure 5
Conformational transition of the Pf1 coat protein from a membrane-bound form to its structural form in bacteriophage particles. Stereo pairs (left, right) are shown for each panel. (A) Molecular surface representation of a 27-subunit repeat of the Pf1 bacteriophage particle showing the interacting subunits (i, i±5, i±6, and i-11). Subunit i is shown in yellow. The yellow circle highlights the proximity of D4 (red) in subunit i, and K20 (blue) in subunit i-11. (B) K20 positive charges (blue) from phage subunits i, i+5, and i+6 are free to interact with a new incoming subunit. These side-chain interactions with the acidic N-terminal region of the membrane-bound form of Pf1 coat protein (green) could guide it to the i+11 subunit position on the growing bacteriophage particle. (C) Additional interactions between the basic C-terminal portion of the coat protein and the bacteriophage DNA, and between neighboring hydrophobic C-terminal helices may trigger the conformational change in the inter-helical loop in the membrane-bound form of the protein and α-helix in the structural form of the protein, upon addition of the i+11 subunit (green) to the growing bacteriophage particle. (D) The newly incorporated i+11 subunit (green) interacts with its neighboring subunits i (yellow), i+5, and i+6.

Similar articles

See all similar articles

Cited by 32 articles

See all "Cited by" articles

Publication types

LinkOut - more resources

Feedback