title: Structural insights into the activation of the RhoA GTPase by the lymphoid blast crisis (Lbc) oncoprotein.
abstract: The small GTPase RhoA promotes deregulated signaling upon interaction with lymphoid blast crisis (Lbc), the oncogenic form of A-kinase anchoring protein 13 (AKAP13). The onco-Lbc protein is a hyperactive Rho-specific guanine nucleotide exchange factor (GEF), but its structural mechanism has not been reported despite its involvement in cardiac hypertrophy and cancer causation. The pleckstrin homology (PH) domain of Lbc is located at the C-terminal end of the protein and is shown here to specifically recognize activated RhoA rather than lipids. The isolated dbl homology (DH) domain can function as an independent activator with an enhanced activity. However, the DH domain normally does not act as a solitary Lbc interface with RhoA-GDP. Instead it is negatively controlled by the PH domain. In particular, the DH helical bundle is coupled to the structurally dependent PH domain through a helical linker, which reduces its activity. Together the two domains form a rigid scaffold in solution as evidenced by small angle x-ray scattering and (1)H,(13)C,(15)N-based NMR spectroscopy. The two domains assume a "chair" shape with its back possessing independent GEF activity and the PH domain providing a broad seat for RhoA-GTP docking rather than membrane recognition. This provides structural and dynamical insights into how DH and PH domains work together in solution to support regulated RhoA activity. Mutational analysis supports the bifunctional PH domain mediation of DH-RhoA interactions and explains why the tandem domain is required for controlled GEF signaling.
authors.affiliation: From the School of Cancer Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom.
authors.forename: Marc
authors.initials: M
authors.lastname: Lenoir
authors.affiliation: From the School of Cancer Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom.
authors.forename: Masae
authors.initials: M
authors.lastname: Sugawara
authors.affiliation: From the School of Cancer Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom.
authors.forename: Jaswant
authors.initials: J
authors.lastname: Kaur
authors.affiliation: Structural Genomics Consortium, University of Oxford, Oxford OX3 7DQ, United Kingdom, and The Leibniz Institute of Molecular Pharmacology, Campus Buch, 13125 Berlin, Germany.
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Ball
authors.affiliation: From the School of Cancer Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom, m.overduin@bham.ac.uk.
authors.forename: Michael
authors.initials: M
authors.lastname: Overduin
mesh_terms: D054758:A Kinase Anchor Proteins / Q000235:genetics / Q000502:physiology*; D000595:Amino Acid Sequence; D018076:DNA, Complementary; D004789:Enzyme Activation; D006801:Humans; D015778:Minor Histocompatibility Antigens; D008969:Molecular Sequence Data; D009154:Mutation; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D020742:rhoA GTP-Binding Protein / Q000737:chemistry / Q000378:metabolism*
chemical_list: D054758:A Kinase Anchor Proteins; C085467:AKAP13 protein, human; D018076:DNA, Complementary; D015778:Minor Histocompatibility Antigens; D011518:Proto-Oncogene Proteins; D020742:rhoA GTP-Binding Protein
keywords: AKAP; GTPase; Guanine Nucleotide Exchange Factor (GEF); Lbc; Nuclear Magnetic Resonance; Oncogene; Protein Structure; Protein-Protein Interaction; Ras Homolog Gene Family, Member A (RhoA); Rho GTPases