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Homodimeric Protein (homodimeric + protein)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Actin filament binding by a monomeric IQGAP1 fragment with a single calponin homology domain

CYTOSKELETON, Issue 4 2004
Scott C. Mateer
Abstract IQGAP1 is a homodimeric protein that reversibly associates with F-actin, calmodulin, activated Cdc42 and Rac1, CLIP-170, ,-catenin, and E-cadherin. Its F-actin binding site includes a calponin homology domain (CHD) located near the N-terminal of each subunit. Prior studies have implied that medium- to high-affinity F-actin binding (5,50 ,M Kd) requires multiple CHDs located either on an individual polypeptide or on distinct subunits of a multimeric protein. For IQGAP1, a series of six tandem IQGAP coiled-coil repeats (IRs) located past the C-terminal of the CHD of each subunit support protein dimerization and, by extension, the IRs or an undefined subset of them were thought to be essential for F-actin binding mediated by its CHDs. Here we describe efforts to determine the minimal region of IQGAP1 capable of binding F-actin. Several truncation mutants of IQGAP1, which contain progressive deletions of the IRs and CHD, were assayed for F-actin binding in vitro. Fragments that contain both the CHD and at least one IR could bind F-actin and, as expected, removal of all six IRs and the CHD abolished binding. Unexpectedly, a fragment called IQGAP12-210, which contains the CHD, but lacks IRs, could bind actin filaments. IQGAP12-210 was found to be monomeric, to bind F-actin with a Kd of ,47 ,M, to saturate F-actin at a molar ratio of one IQGAP12-210 per actin monomer, and to co-localize with cortical actin filaments when expressed by transfection in cultured cells. These collective results identify the first known example of high-affinity actin filament binding mediated by a single CHD. Cell Motil. Cytoskeleton 58:231,241, 2004. © 2004 Wiley-Liss, Inc. [source]

Escherichia coli Hsp31 functions as a holding chaperone that cooperates with the DnaK-DnaJ-GrpE system in the management of protein misfolding under severe stress conditions

MOLECULAR MICROBIOLOGY, Issue 3 2004
Mirna Mujacic
Summary Escherichia coli Hsp31 is a homodimeric protein that exhibits chaperone activity in vitro and is a representative member of a recently recognized family of heat shock proteins (Hsps). To gain insights on Hsp31 cellular function, we deleted the hchA gene from the MC4100 chromosome and combined the resulting null allele with lesions in other cytoplasmic chaperones. Although the hchA mutant only exhibited growth defects when cultivated at 48°C, loss of Hsp31 had a strong deleterious effect on the ability of cells to survive and recover from transient exposure to 50°C, and led to the enhanced aggregation of a subset of host proteins at this temperature. The absence of Hsp31 did not significantly affect the ability of the ClpB-DnaK-DnaJ-GrpE system to clear thermally aggregated proteins at 30°C suggesting that Hsp31 does not possess disaggregase activity. Although it had no effect on the growth of groES30, ,clpB or ,ibpAB cells at high temperatures, the hchA deletion aggravated the temperature sensitive phenotype of dnaK756 and grpE280 mutants and led to increased aggregation in stressed dnaK756 cells. On the basis of biochemical, structural and genetic data, we propose that Hsp31 acts as a modified holding chaperone that captures early unfolding intermediates under prolonged conditions of severe stress and releases them when cells return to physiological conditions. This additional line of defence would complement the roles of DnaK-DnaJ-GrpE, ClpB and IbpB in the management of thermally induced cellular protein misfolding. [source]

Crystallization and preliminary X-ray analyses of catabolite control protein A, free and in complex with its DNA-binding site

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2000
Jan Tebbe
The catabolite control protein (CcpA) from Bacillus megaterium is a member of the bacterial repressor protein family GalR/LacI. CcpA with an N-terminal His-tag was used for crystallization. Crystals of free CcpA and of CcpA in complex with the putative operator sequence (catabolite responsive elements, CRE) were obtained by vapour-diffusion techniques at 291,K using the hanging-drop method. CcpA crystals grown in the presence of polyethylene glycol 8000 belong to the hexagonal space group P6122 or P6522, with unit-cell parameters a = 74.4, c = 238.8,Å. These crystals diffract X-rays to 2.55,Å resolution and contain one monomer of the homodimeric protein per asymmetric unit. Crystals of the CcpA,CRE complex were obtained with ammonium sulfate as precipitant and belong to the tetragonal space group I4122, with unit-cell parameters a = 125, c = 400,Å and one complex per asymmetric unit. Although these co-crystals grew to a sufficient size, X-ray diffraction was limited to 8,Å resolution. [source]

Macromolecular recognition in the Protein Data Bank

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2007
Joël Janin
Crystal structures deposited in the Protein Data Bank illustrate the diversity of biological macromolecular recognition: transient interactions in protein,protein and protein,DNA complexes and permanent assemblies in homodimeric proteins. The geometric and physical chemical properties of the macromolecular interfaces that may govern the stability and specificity of recognition are explored in complexes and homodimers compared with crystal-packing interactions. It is found that crystal-packing interfaces are usually much smaller; they bury fewer atoms and are less tightly packed than in specific assemblies. Standard-size interfaces burying 1200,2000,Å2 of protein surface occur in protease,inhibitor and antigen,antibody complexes that assemble with little or no conformation changes. Short-lived electron-transfer complexes have small interfaces; the larger size of the interfaces observed in complexes involved in signal transduction and homodimers correlates with the presence of conformation changes, often implicated in biological function. Results of the CAPRI (critical assessment of predicted interactions) blind prediction experiment show that docking algorithms efficiently and accurately predict the mode of assembly of proteins that do not change conformation when they associate. They perform less well in the presence of large conformation changes and the experiment stimulates the development of novel procedures that can handle such changes. [source]