2ke5
Solution structure and dynamics of the small GTPase Ralb in its active conformation: significance for effector protein binding
Structural highlights
FunctionRALB_HUMAN Multifunctional GTPase involved in a variety of cellular processes including gene expression, cell migration, cell proliferation, oncogenic transformation and membrane trafficking. Accomplishes its multiple functions by interacting with distinct downstream effectors. Acts as a GTP sensor for GTP-dependent exocytosis of dense core vesicles. Required both to stabilize the assembly of the exocyst complex and to localize functional exocyst complexes to the leading edge of migrating cells. Plays a role in the late stages of cytokinesis and is required for the abscission of the bridge joining the sister cells emerging from mitosis. Required for suppression of apoptosis.[1] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe small G proteins RalA/B have a crucial function in the regulatory network that couples extracellular signals with appropriate cellular responses. RalA/B are an important component of the Ras signalling pathway and in addition to their role in membrane trafficking, are implicated in the initiation and maintenance of tumourigenic transformation of human cells. RalA and RalB share 85% sequence identity and collaborate in supporting cancer cell proliferation but have markedly different effects. RalA is important in mediating proliferation, while depletion of RalB results in transformed cells undergoing apoptosis. Crystal structures of RalA in the free form and in complex with its effectors, Sec5 and Exo84 have been solved. Here we have determined the solution structure of free RalB bound to the GTP analogue GMPPNP to an RMSD of 0.6 ?. We show that, while the overall architecture of RalB is very similar to the crystal structure of RalA, differences exist in the switch regions, which are sensitive to the bound nucleotide. Backbone 15N dynamics suggest that there are four regions of disorder in RalB: the P-loop, switch I, switch II and the loop comprising residues 116-121, which has a single residue insertion compared to RalA, 31P NMR data and the structure of RalB?GMPPNP show that the switch regions predominantly adopt state 1 (Ras nomenclature) in the unbound form, which in Ras is not competent to bind effectors. In contrast, 31P NMR analysis of RalB?GTP reveals that conformations corresponding to states 1 and 2 are both sampled in solution and that addition of an effector protein only partially stabilises state 2. Solution structure and dynamics of the small GTPase RalB in its active conformation: significance for effector protein binding.,Fenwick R, Prasannan S, Campbell L, Nietlispach D, Evetts K, Camonis J, Mott H, Owen D Biochemistry. 2009 Jan 23. PMID:19166349[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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