We have recorded X-ray diffraction patterns at 3.1 A resolution from magnetically aligned fibres of the Pf3 strain of filamentous bacteriophage (Inovirus). The patterns are similar to patterns from the higher-temperature form of the Pf1 strain, indicating that the Pf3 and Pf1 virions have the same helix symmetry and similar protein subunit shape ...
We have recorded X-ray diffraction patterns at 3.1 A resolution from magnetically aligned fibres of the Pf3 strain of filamentous bacteriophage (Inovirus). The patterns are similar to patterns from the higher-temperature form of the Pf1 strain, indicating that the Pf3 and Pf1 virions have the same helix symmetry and similar protein subunit shape. This is of particular interest, given that the primary structures of the two protein subunits are quite different; and the nucleotide/protein subunit ratio in the Pf3 virion is more than twice that in Pf1, indicating important differences in DNA packaging. We have built a molecular model of the Pf3 protein capsid based on the model of Pf1, and refined it against the diffraction data using simulated annealing. The refinement confirms that the two structures are similar, which may reflect a fundamental motif of alpha-helix packing. However, there are some differences between the structures: the Pf3 subunit appears to be completely alpha-helical, beginning at the N terminus, whereas the first few residues of the Pf1 subunit are not helical; and the structure of the C-terminal region of the Pf3 subunit at the inner surface of the tubular capsid indicates that DNA/protein interactions in this virion may involve both aromatic side-chains and positively charged side-chains, whereas those in the Pf1 virion involve predominantly only the latter. In the course of this work, we have developed new approaches to refinement and validation of helical structures with respect to continuous transform fibre diffraction data.
Related Citations:
Pf1 Filamentous Bacteriophage: Refinement of a Molecular Model by Simulated Annealing Using 3.3 A Resolution X-Ray Fibre Diffraction Data Gonzalez, A., Nave, C., Marvin, D.A. (1995) Acta Crystallogr D Biol Crystallogr 51: 792
Two Forms of Pf1 Inovirus: X-Ray Diffraction Studies on a Structural Phase Transition and a Calculated Libration Normal Mode of the Asymmetric Unit Marvin, D.A., Nave, C., Bansal, M., Hale, R.D., Salje, E.K.H. (1992) Ph Transit 39: 45
Model-Building Studies of Inovirus: Genetic Variations on a Geometric Theme Marvin, D.A. (1990) Int J Biol Macromol 12: 125
Erratum. Model-Building Studies of Inovirus: Genetic Variations on a Geometric Theme Marvin, D.A. (1990) Int J Biol Macromol 12: 335
Dynamics of Telescoping Inovirus: A Mechanism for Assembly at Membrane Adhesions Marvin, D.A. (1989) Int J Biol Macromol 11: 159
Organizational Affiliation:
Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge, CB2 1GA, UK.
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