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1.  Bacteriophage P23-77 Capsid Protein Structures Reveal the Archetype of an Ancient Branch from a Major Virus Lineage 
Structure(London, England:1993)  2013;21(5):718-726.
It has proved difficult to classify viruses unless they are closely related since their rapid evolution hinders detection of remote evolutionary relationships in their genetic sequences. However, structure varies more slowly than sequence, allowing deeper evolutionary relationships to be detected. Bacteriophage P23-77 is an example of a newly identified viral lineage, with members inhabiting extreme environments. We have solved multiple crystal structures of the major capsid proteins VP16 and VP17 of bacteriophage P23-77. They fit the 14 Å resolution cryo-electron microscopy reconstruction of the entire virus exquisitely well, allowing us to propose a model for both the capsid architecture and viral assembly, quite different from previously published models. The structures of the capsid proteins and their mode of association to form the viral capsid suggest that the P23-77-like and adeno-PRD1 lineages of viruses share an extremely ancient common ancestor.
•High-resolution structures of the two major capsid proteins of bacteriophage P23-77•P23-77 capsid proteins exhibit a conserved single β-barrel core fold•P23-77 is an ancient relative of the double β-barrel lineage of viruses•Capsid model illustrates that P23-77 uses a novel method of organization
Rissanen et al. propose a model for the architecture and assembly of bacteriophage P23-77 quite different from those previously published. The capsid proteins and their mode of association to form the virus particle suggest that P23-77 share a common evolutionary origin with the PRD1/Adenovirus lineage.
PMCID: PMC3919167  PMID: 23623731
2.  Crystallization and preliminary crystallographic analysis of the major capsid proteins VP16 and VP17 of bacteriophage P23-77 
The major capsid proteins VP16 and VP17 of bacteriophage P23-77 have been crystallized using both recombinant and purified virus and preliminary diffraction analyses have been performed.
Members of the diverse double-β-barrel lineage of viruses are identified by the conserved structure of their major coat protein. New members of this lineage have been discovered based on structural analysis and we are interested in identifying relatives that utilize unusual versions of the double-β-barrel fold. One candidate for such studies is P23-77, an icosahedral dsDNA bacteriophage that infects the extremophile Thermus thermophilus. P23-77 has two major coat proteins, namely VP16 and VP17, of a size consistent with a single-β-barrel core fold. These previously unstudied proteins have now been successfully expressed as recombinant proteins, purified and crystallized using hanging-drop and sitting-drop vapour-diffusion methods. Crystals of coat proteins VP16 and VP17 have been obtained as well as of a putative complex. In addition, virus-derived material has been crystallized. Diffraction data have been collected to beyond 3 Å resolution for five crystal types and structure determinations are in progress.
PMCID: PMC3374517  PMID: 22691792
bacteriophages; capsid proteins
3.  A Unique Group of Virus-Related, Genome-Integrating Elements Found Solely in the Bacterial Family Thermaceae and the Archaeal Family Halobacteriaceae▿ †  
Journal of Bacteriology  2010;192(12):3231-3234.
Viruses SH1 and P23-77, infecting archaeal Haloarcula species and bacterial Thermus species, respectively, were recently designated to form a novel viral lineage. In this study, the lineage is expanded to archaeal Halomicrobium and bacterial Meiothermus species by analysis of five genome-integrated elements that share the core genes with these viruses.
PMCID: PMC2901701  PMID: 20400546
4.  Yeast Two-Hybrid Studies on Interaction of Proteins Involved in Regulation of Nitrogen Fixation in the Phototrophic Bacterium Rhodobacter capsulatus 
Journal of Bacteriology  2003;185(17):5240-5247.
Rhodobacter capsulatus contains two PII-like proteins, GlnB and GlnK, which play central roles in controlling the synthesis and activity of nitrogenase in response to ammonium availability. Here we used the yeast two-hybrid system to probe interactions between these PII-like proteins and proteins known to be involved in regulating nitrogen fixation. Analysis of defined protein pairs demonstrated the following interactions: GlnB-NtrB, GlnB-NifA1, GlnB-NifA2, GlnB-DraT, GlnK-NifA1, GlnK-NifA2, and GlnK-DraT. These results corroborate earlier genetic data and in addition show that PII-dependent ammonium regulation of nitrogen fixation in R. capsulatus does not require additional proteins, like NifL in Klebsiella pneumoniae. In addition, we found interactions for the protein pairs GlnB-GlnB, GlnB-GlnK, NifA1-NifA1, NifA2-NifA2, and NifA1-NifA2, suggesting that fine tuning of the nitrogen fixation process in R. capsulatus may involve the formation of GlnB-GlnK heterotrimers as well as NifA1-NifA2 heterodimers. In order to identify new proteins that interact with GlnB and GlnK, we constructed an R. capsulatus genomic library for use in yeast two-hybrid studies. Screening of this library identified the ATP-dependent helicase PcrA as a new putative protein that interacts with GlnB and the Ras-like protein Era as a new protein that interacts with GlnK.
PMCID: PMC181009  PMID: 12923097

Results 1-4 (4)