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Phage Phenomics: Physiological Approaches to Characterize Novel Viral Proteins
09:40

Phage Phenomics: Physiological Approaches to Characterize Novel Viral Proteins

Published on: June 11, 2015

The protein capsid of filamentous bacteriophage PH75 from Thermus thermophilus

D M Pederson1, L C Welsh, D A Marvin

  • 1Cambridge Centre for Molecular Recognition, Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK.

Journal of Molecular Biology
|May 24, 2001
PubMed

Insights

Filamentous bacteriophage PH75 from Thermus thermophilus shares structural similarities with other Inoviruses despite different assembly temperatures and coat protein sequences. This suggests a conserved alpha-helix packing motif in viral capsid design.

Area of Science:

  • Structural biology
  • Virology
  • Biophysics

Background:

  • Filamentous bacteriophages, or Inoviruses, infect bacteria and possess unique protein capsid structures.
  • The PH75 bacteriophage infects the thermophilic bacterium Thermus thermophilus, assembling at high temperatures (70°C).
  • Comparison with mesophilic bacteriophages like Pf1 and Pf3 provides insights into conserved viral assembly mechanisms.

Purpose of the Study:

  • To characterize the PH75 bacteriophage, focusing on its viral DNA and major coat protein (p8).
  • To investigate the structural similarities and differences between PH75 and other Inoviruses.
  • To build and refine a molecular model of the PH75 protein capsid.

Main Methods:

  • Amino acid sequencing of the PH75 major coat protein (p8).
  • X-ray fiber diffraction analysis of ordered PH75 virions.
  • Molecular modeling and simulated annealing refinement using diffraction data (up to 2.4 Å meridional, 3.1 Å equatorial resolution).

Main Results:

  • The PH75 p8 protein lacks a leader sequence, differing from Pf1 but similar to Pf3.
  • X-ray diffraction patterns reveal that the PH75 capsid shares helical symmetry and subunit shape with Pf1 and Pf3.
  • A refined molecular model of the PH75 capsid was generated, highlighting conserved alpha-helix packing despite sequence divergence.

Conclusions:

  • The PH75 bacteriophage exhibits a conserved capsid structure with other Inoviruses, suggesting a fundamental alpha-helix packing motif.
  • Differences in coat protein sequence and assembly temperatures point to variations in assembly mechanisms and host interactions.
  • Further investigation is needed to understand variations in DNA packaging and coat protein insertion into the host membrane.

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