Primary Citation of Related Structures: 1QL1, 1QL2
PubMed Abstract:
The major coat protein in the capsid of Pf1 filamentous bacteriophage (Inovirus) forms a helical assembly of about 7000 identical protein subunits, each of which contains 46 amino-acid residues and can be closely approximated by a single gently curved alpha-helix ...
The major coat protein in the capsid of Pf1 filamentous bacteriophage (Inovirus) forms a helical assembly of about 7000 identical protein subunits, each of which contains 46 amino-acid residues and can be closely approximated by a single gently curved alpha-helix. Since the viral DNA occupies the core of the tubular capsid and appears to make no significant specific interactions with the capsid proteins, the capsid is a simple model system for the study of the static and dynamic properties of alpha-helix assembly. The capsid undergoes a reversible temperature-induced structural transition at about 283 K between two slightly different helix forms. The two forms can coexist without an intermediate state, consistent with a first-order structural phase transition. The molecular model of the higher temperature form was refined using improved X-ray fibre diffraction data and new refinement and validation methods. The refinement indicates that the two forms are related by a change in the orientation of the capsid subunits within the virion, without a significant change in local conformation of the subunits. On the higher temperature diffraction pattern there is a region of observed intensity that is not consistent with a simple helix of identical subunits; it is proposed that the structure involves groups of three subunits which each have a slightly different orientation within the group. The grouping of subunits suggests that a change in subunit libration frequency could be the basis of the Pf1 structural transition; calculations from the model are used to explore this idea.
Related Citations:
Pf1 Filamentous Bacteriophage: Refinement of a Molecular Model by Simulated Annealing Using 3.3 Angstroms 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
Dynamics of Telescoping Inovirus: A Mechanism for Assembly at Membrane Adhesions Marvin, D.A. (1989) Int J Biol Macromol 11: 159
Organizational Affiliation:
Cambridge Centre for Molecular Recognition, Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, England.
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