title: Solution structure of the SGTA dimerisation domain and investigation of its interactions with the ubiquitin-like domains of BAG6 and UBL4A.
abstract: BACKGROUND
  The BAG6 complex resides in the cytosol and acts as a sorting point to target diverse hydrophobic protein substrates along their appropriate paths, including proteasomal degradation and ER membrane insertion. Composed of a trimeric complex of BAG6, TRC35 and UBL4A, the BAG6 complex is closely associated with SGTA, a co-chaperone from which it can obtain hydrophobic substrates.
  
  
  RESULTS
  SGTA consists of an N-terminal dimerisation domain (SGTA_NT), a central tetratricopeptide repeat (TPR) domain, and a glutamine rich region towards the C-terminus. Here we solve a solution structure of the SGTA dimerisation domain and use biophysical techniques to investigate its interaction with two different UBL domains from the BAG6 complex. The SGTA_NT structure is a dimer with a tight hydrophobic interface connecting two sets of four alpha helices. Using a combination of NMR chemical shift perturbation, isothermal titration calorimetry (ITC) and microscale thermophoresis (MST) experiments we have biochemically characterised the interactions of SGTA with components of the BAG6 complex, the ubiquitin-like domain (UBL) containing proteins UBL4A and BAG6. We demonstrate that the UBL domains from UBL4A and BAG6 directly compete for binding to SGTA at the same site. Using a combination of structural and interaction data we have implemented the HADDOCK protein-protein interaction docking tool to generate models of the SGTA-UBL complexes.
  
  
  CONCLUSIONS
  This atomic level information contributes to our understanding of the way in which hydrophobic proteins have their fate decided by the collaboration between SGTA and the BAG6 complex.
authors.affiliation: Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London, SE1 1DB, United Kingdom.
authors.forename: John F
authors.initials: JF
authors.lastname: Darby
authors.affiliation: Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London, SE1 1DB, United Kingdom.
authors.forename: Ewelina M
authors.initials: EM
authors.lastname: Krysztofinska
authors.affiliation: Division of Molecular Biosciences, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ, United Kingdom; Bruker U.K. Ltd, Banner Lane, Coventry CV4 9GH, United Kingdom.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Simpson
authors.affiliation: Division of Molecular Biosciences, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ, United Kingdom.
authors.forename: Aline C
authors.initials: AC
authors.lastname: Simon
authors.affiliation: Faculty of Life Sciences, University of Manchester, The Michael Smith Building, Oxford Road, Manchester, M13 9PT, United Kingdom.
authors.forename: Pawel
authors.initials: P
authors.lastname: Leznicki
authors.affiliation: Division of Molecular Biosciences, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ, United Kingdom.
authors.forename: Newran
authors.initials: N
authors.lastname: Sriskandarajah
authors.affiliation: Division of Molecular Biosciences, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ, United Kingdom.
authors.forename: David S
authors.initials: DS
authors.lastname: Bishop
authors.affiliation: Division of Molecular Biosciences, Imperial College London, Exhibition Road, South Kensington, London, SW7 2AZ, United Kingdom.
authors.forename: Lisa R
authors.initials: LR
authors.lastname: Hale
authors.affiliation: Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London, SE1 1DB, United Kingdom.
authors.forename: Caterina
authors.initials: C
authors.lastname: Alfano
authors.affiliation: Randall Division of Cell and Molecular Biophysics, King's College London, New Hunt's House, London SE1 1UL, United Kingdom.
authors.forename: Maria R
authors.initials: MR
authors.lastname: Conte
authors.affiliation: Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London, SE1 1DB, United Kingdom.
authors.forename: Santiago
authors.initials: S
authors.lastname: Martínez-Lumbreras
authors.affiliation: Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London, SE1 1DB, United Kingdom.
authors.forename: Arjun
authors.initials: A
authors.lastname: Thapaliya
authors.affiliation: Faculty of Life Sciences, University of Manchester, The Michael Smith Building, Oxford Road, Manchester, M13 9PT, United Kingdom.
authors.forename: Stephen
authors.initials: S
authors.lastname: High
authors.affiliation: Department of Chemistry, King's College London, Britannia House, 7 Trinity Street, London, SE1 1DB, United Kingdom.
authors.forename: Rivka L
authors.initials: RL
authors.lastname: Isaacson
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D019295:Computational Biology / Q000379:methods; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D025941:Protein Interaction Mapping / Q000379:methods; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D012984:Software; D012996:Solutions; D025801:Ubiquitin / Q000737:chemistry / Q000378:metabolism; D014452:Ubiquitins / Q000737:chemistry* / Q000378:metabolism
chemical_list: C092009:BAG6 protein, human; D002352:Carrier Proteins; D018832:Molecular Chaperones; D046912:Multiprotein Complexes; C114575:SGTA protein, human; D012996:Solutions; D025801:Ubiquitin; D014452:Ubiquitins; C583268:Ubl4A protein, human