title: Trp RNA-binding attenuation protein: modifying symmetry and stability of a circular oligomer.
abstract: BACKGROUND
  Subunit number is amongst the most important structural parameters that determine size, symmetry and geometry of a circular protein oligomer. The L-tryptophan biosynthesis regulator, TRAP, present in several Bacilli, is a good model system for investigating determinants of the oligomeric state. A short segment of C-terminal residues defines whether TRAP forms an 11-mer or 12-mer assembly. To understand which oligomeric state is more stable, we examine the stability of several wild type and mutant TRAP proteins.
  
  
  RESULTS
  Among the wild type B. stearothermophilus, B. halodurans and B. subtilis TRAP, we find that the former is the most stable whilst the latter is the least. Thermal stability of all TRAP is shown to increase with L-tryptophan concentration. We also find that mutant TRAP molecules that are truncated at the C-terminus - and hence induced to form 12-mers, distinct from their 11-mer wild type counterparts--have increased melting temperatures. We show that the same effect can be achieved by a point mutation S72N at a subunit interface, which leads to exclusion of C-terminal residues from the interface. Our findings are supported by dye-based scanning fluorimetry, CD spectroscopy, and by crystal structure and mass spectrometry analysis of the B. subtilis S72N TRAP.
  
  
  CONCLUSIONS
  We conclude that the oligomeric state of a circular protein can be changed by introducing a point mutation at a subunit interface. Exclusion (or deletion) of the C-terminus from the subunit interface has a major impact on properties of TRAP oligomers, making them more stable, and we argue that the cause of these changes is the altered oligomeric state. The more stable TRAP oligomers could be used in potential applications of TRAP in bionanotechnology.
authors.affiliation: York Structural Biology Laboratory, Department of Chemistry, University of York, York, United Kingdom.
authors.forename: Oliver W
authors.initials: OW
authors.lastname: Bayfield
authors.forename: Chao-Sheng
authors.initials: CS
authors.lastname: Chen
authors.forename: Andrea R
authors.initials: AR
authors.lastname: Patterson
authors.forename: Weisha
authors.initials: W
authors.lastname: Luan
authors.forename: Callum
authors.initials: C
authors.lastname: Smits
authors.forename: Paul
authors.initials: P
authors.lastname: Gollnick
authors.forename: Alfred A
authors.initials: AA
authors.lastname: Antson
mesh_terms: D001412:Bacillus subtilis / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D007700:Kinetics; D013058:Mass Spectrometry; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*; D044366:Transition Temperature; D014364:Tryptophan / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C079092:MtrB protein, Bacteria; D050505:Mutant Proteins; D021122:Protein Subunits; D016601:RNA-Binding Proteins; D014157:Transcription Factors; D014364:Tryptophan