title: Defining the Intrinsically Disordered C-Terminal Domain of SSB Reveals DNA-Mediated Compaction.
abstract: The bacterial single-stranded DNA (ssDNA) binding protein SSB is a strictly conserved and essential protein involved in diverse functions of DNA metabolism, including replication and repair. SSB comprises a well-characterized tetrameric core of N-terminal oligonucleotide binding OB folds that bind ssDNA and four intrinsically disordered C-terminal domains of unknown structure that interact with partner proteins. The generally accepted, albeit speculative, mechanistic model in the field postulates that binding of ssDNA to the OB core induces the flexible, undefined C-terminal arms to expand outwards encouraging functional interactions with partner proteins. In this structural study, we show that the opposite is true. Combined small-angle scattering with X-rays and neutrons coupled to coarse-grained modeling reveal that the intrinsically disordered C-terminal arms are relatively collapsed around the tetrameric OB core and collapse further upon ssDNA binding. This implies a mechanism of action, in which the disordered C-terminal domain collapse traps the ssDNA and pulls functional partners onto the ssDNA.
authors.affiliation: Centre for Biomolecular Sciences, School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom.
authors.forename: Matthew
authors.initials: M
authors.lastname: Green
authors.affiliation: ISIS Spallation Neutron and Muon Source, Rutherford Appleton Laboratory, Oxfordshire OX11 0FA, United Kingdom.
authors.forename: Louise
authors.initials: L
authors.lastname: Hatter
authors.affiliation: Department of Biochemistry, MSC 7760, The University of Texas Health Center at San Antonio, 7703 Floyd Curl Drive, San Antonio TX 78229-3900, USA.
authors.forename: Emre
authors.initials: E
authors.lastname: Brookes
authors.affiliation: Centre for Biomolecular Sciences, School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom. Electronic address: panos.soultanas@nottingham.ac.uk.
authors.forename: Panos
authors.initials: P
authors.lastname: Soultanas
authors.affiliation: ISIS Spallation Neutron and Muon Source, Rutherford Appleton Laboratory, Oxfordshire OX11 0FA, United Kingdom; School of Biosciences, University of Nottingham, Sutton Bonington Campus, Leicestershire LE12 5RD, United Kingdom; Research Complex at Harwell, Rutherford Appleton Laboratory, Oxfordshire OX11 0FA, United Kingdom. Electronic address: david.scott@nottingham.ac.uk.
authors.forename: David J
authors.initials: DJ
authors.lastname: Scott
mesh_terms: D001412:Bacillus subtilis / Q000737:chemistry*; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D053838:Scattering, Small Angle
chemical_list: D004268:DNA-Binding Proteins; D004247:DNA
keywords: Bacillus subtilis; SANS; SASSIE; SAXS; intrinsic disorder