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Structure of a signal transduction regulator, RACK1, from Arabidopsis thaliana.

ABSTRACT: The receptor for activated C-kinase 1 (RACK1) is a highly conserved WD40 repeat scaffold protein found in a wide range of eukaryotic species from Chlamydymonas to plants and humans. In tissues of higher mammals, RACK1 is ubiquitously expressed and has been implicated in diverse signaling pathways involving neuropathology, cellular stress, protein translation, and developmental processes. RACK1 has established itself as a scaffold protein through physical interaction with a myriad of signaling proteins ranging from kinases, phosphatases, ion channels, membrane receptors, G proteins, IP3 receptor, and with widely conserved structural proteins associated with the ribosome. In the plant Arabidopsis thaliana, RACK1A is implicated in diverse developmental and environmental stress pathways. Despite the functional conservation of RACK1-mediated protein-protein interaction-regulated signaling modes, the structural basis of such interactions is largely unknown. Here we present the first crystal structure of a RACK1 protein, RACK1 isoform A from Arabidopsis thaliana, at 2.4 A resolution, as a C-terminal fusion of the maltose binding protein. The structure implicates highly conserved surface residues that could play critical roles in protein-protein interactions and reveals the surface location of proposed post-transcriptionally modified residues. The availability of this structure provides a structural basis for dissecting RACK1-mediated cellular signaling mechanisms in both plants and animals.

SUBMITTER: Ullah H

PROVIDER: S-EPMC2548356 | biostudies-literature | 2008 Oct

REPOSITORIES: biostudies-literature

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Structure of a signal transduction regulator, RACK1, from Arabidopsis thaliana.

Ullah Hemayet H Scappini Erica Louise EL Moon Andrea Florence AF Williams Latanya Veronica LV Armstrong David Lee DL Pedersen Lars Christian LC

Protein science : a publication of the Protein Society 20080820 10

The receptor for activated C-kinase 1 (RACK1) is a highly conserved WD40 repeat scaffold protein found in a wide range of eukaryotic species from Chlamydymonas to plants and humans. In tissues of higher mammals, RACK1 is ubiquitously expressed and has been implicated in diverse signaling pathways involving neuropathology, cellular stress, protein translation, and developmental processes. RACK1 has established itself as a scaffold protein through physical interaction with a myriad of signaling pr ...[more]

PMID: 18715992

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Project description:UNLABELLED:Bacteriophytochrome photoreceptors (BphPs) and their cognate response regulators make up two-component signal transduction systems which direct bacteria to mount phenotypic responses to changes in environmental light quality. Most of these systems utilize single-domain response regulators to transduce signals through unknown pathways and mechanisms. Here we describe the photocycle and autophosphorylation kinetics of RtBphP1, a red light-regulated histidine kinase from the desert bacterium Ramlibacter tataouinensis RtBphP1 undergoes red to far-red photoconversion with rapid thermal reversion to the dark state. RtBphP1 is autophosphorylated in the dark; this activity is inhibited under red light. The RtBphP1 cognate response regulator, the R. tataouinensis bacteriophytochrome response regulator (RtBRR), and a homolog, AtBRR from Agrobacterium tumefaciens, crystallize unexpectedly as arm-in-arm dimers, reliant on a conserved hydrophobic motif, hFWAhL (where h is a hydrophobic M, V, L, or I residue). RtBRR and AtBRR dimerize distinctly from four structurally characterized phytochrome response regulators found in photosynthetic organisms and from all other receiver domain homodimers in the Protein Data Bank. A unique cacodylate-zinc-histidine tag metal organic framework yielded single-wavelength anomalous diffraction phases and may be of general interest. Examination of the effect of the BRR stoichiometry on signal transduction showed that phosphorylated RtBRR is accumulated more efficiently than the engineered monomeric RtBRR (RtBRRmon) in phosphotransfer reactions. Thus, we conclude that arm-in-arm dimers are a relevant signaling intermediate in this class of two-component regulatory systems. IMPORTANCE:BphP histidine kinases and their cognate response regulators comprise widespread red light-sensing two-component systems. Much work on BphPs has focused on structural understanding of light sensing and on enhancing the natural infrared fluorescence of these proteins, rather than on signal transduction or the resultant phenotypes. To begin to address this knowledge gap, we solved the crystal structures of two single-domain response regulators encoded by a region immediately downstream of that encoding BphPs. We observed a previously unknown arm-in-arm dimer linkage. Monomerization via deletion of the C-terminal dimerization motif had an inhibitory effect on net response regulator phosphorylation, underlining the importance of these unusual dimers for signal transduction.

Dataset Information

Structure of a signal transduction regulator, RACK1, from Arabidopsis thaliana.

Publications

Structure of a signal transduction regulator, RACK1, from Arabidopsis thaliana.

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