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How to Change the Oligomeric State of a Circular Protein Assembly: Switch from 11-Subunit to 12-Subunit TRAP Suggests a General Mechanism

DOI: 10.1371/journal.pone.0025296 DOI Help
PMID: 21984911 PMID Help

Authors: Chao-Sheng Chen (University of York) , Callum Smits (University of York) , Guy Clarkson (University of York) , Mikhail Shevtsov (University of York) , Natalie Merlino , Paul Gollnick , Fred Antson (University of York) , Eugene A. Permyakov
Co-authored by industrial partner: No

Type: Journal Paper
Journal: PLoS ONE , VOL 6 (10)

State: Published (Approved)
Published: October 2011

Open Access Open Access

Abstract: Background Many critical cellular functions are performed by multisubunit circular protein oligomers whose internal geometry has evolved to meet functional requirements. The subunit number is arguably the most critical parameter of a circular protein assembly, affecting the internal and external diameters of the assembly and often impacting on the protein's function. Although accurate structural information has been obtained for several circular proteins, a lack of accurate information on alternative oligomeric states has prevented engineering such transitions. In this study we used the bacterial transcription regulator TRAP as a model system to investigate the features that define the oligomeric state of a circular protein and to question how the subunit number could be manipulated. Methodology/Principal Findings We find that while Bacillus subtilis and Bacillus stearothermophilus TRAP form 11-subunit oligomers, the Bacillus halodurans TRAP exclusively forms 12-subunit assemblies. Significantly, the two states of TRAP are related by a simple rigid body rotation of individual subunits around inter-subunit axes. We tested if such a rotation could be induced by insertion or deletion mutations at the subunit interface. Using wild type 11-subunit TRAP, we demonstrate that removal of five C-terminal residues at the outer side of the inter-subunit axis or extension of an amino acid side chain at the opposite, inner side, increased the subunit number from 11 to 12. Our findings are supported by crystal structures of TRAP oligomers and by native mass spectrometry data. Conclusions/Significance The subunit number of the TRAP oligomer can be manipulated by introducing deletion or addition mutations at the subunit interface. An analysis of available and emerging structural data on alternative oligomeric states indicates that the same principles may also apply to the subunit number of other circular assemblies suggesting that the deletion/addition approach could be used generally to engineer transitions between different oligomeric states.

Journal Keywords: Amino; Bacillus; Bacterial; Crystallography ; X-Ray ; Geobacillus; Mass; Models ; Molecular ; Protein; Quaternary ; Protein; RNA ; Bacterial ; RNA-Binding; Rotation ; Transcription Factors

Subject Areas: Biology and Bio-materials

Instruments: I24-Microfocus Macromolecular Crystallography

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