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Helix Bundle (helix + bundle)

Distribution by Scientific Domains

Life Sciences	50%
Chemistry	50%

Selected Abstracts

Cold-adapted signal proteins: NMR structures of pheromones from the antarctic ciliate Euplotes nobilii

IUBMB LIFE, Issue 8-9 2007
William J. Placzek
Abstract Cell type-specific signal proteins, known as pheromones, are synthesized by ciliated protozoa in association with their self/nonself mating-type systems, and are utilized to control the vegetative growth and mating stages of their life cycle. In species of the most ubiquitous ciliate, Euplotes, these pheromones form families of structurally homologous molecules, which are constitutively secreted into the extracellular environment, from where they can be isolated in sufficient amounts for chemical characterization. This paper describes the NMR structures of En-1 and En-2, which are members of the cold-adapted pheromone family produced by Euplotes nobilii, a species inhabiting the freezing coastal waters of Antarctica. The structures were determined with the proteins from the natural source, using homonuclear 1H NMR techniques in combination with automated NOESY peak picking and NOE assignment. En-1 and En-2 have highly homologous global folds, which consist of a central three-,-helix bundle with an up-down-up topology and a 310-helical turn near the N-terminus. This fold is stabilized by four disulfide bonds and the helices are connected by bulging loops. Apparent structural specificity resides in the variable C-terminal regions of the pheromones. The NMR structures of En-1 and En-2 provide novel insights into the cold-adaptive modifications that distinguish the E. nobilii pheromone family from the closely related E. raikovi pheromone family isolated from temperate waters. [source]

Solution structure of the region 51,160 of human KIN17 reveals an atypical winged helix domain

PROTEIN SCIENCE, Issue 12 2007
Ludovic Carlier
Abstract Human KIN17 is a 45-kDa eukaryotic DNA- and RNA-binding protein that plays an important role in nuclear metabolism and in particular in the general response to genotoxics. Its amino acids sequence contains a zinc finger motif (residues 28,50) within a 30-kDa N-terminal region conserved from yeast to human, and a 15-kDa C-terminal tandem of SH3-like subdomains (residues 268,393) only found in higher eukaryotes. Here we report the solution structure of the region 51,160 of human KIN17. We show that this fragment folds into a three-,-helix bundle packed against a three-stranded ,-sheet. It belongs to the winged helix (WH) family. Structural comparison with analogous WH domains reveals that KIN17 WH module presents an additional and highly conserved 310 -helix. Moreover, KIN17 WH helix H3 is not positively charged as in classical DNA-binding WH domains. Thus, human KIN17 region 51,160 might rather be involved in protein,protein interaction through its conserved surface centered on the 310 -helix. [source]

The Structural Basis for Docking in Modular Polyketide Biosynthesis

CHEMBIOCHEM, Issue 3 2006
Kira J. Weissman Dr.
Abstract Polyketide natural products such as erythromycin and rapamycin are assembled on polyketide synthases (PKSs), which consist of modular sets of catalytic activities distributed across multiple protein subunits. Correct protein,protein interactions among the PKS subunits which are critical to the fidelity of biosynthesis are mediated in part by "docking domains" at the termini of the proteins. The NMR solution structure of a representative docking domain complex from the erythromycin PKS (DEBS) was recently solved, and on this basis it has been proposed that PKS docking is mediated by the formation of an intermolecular four - ,-helix bundle. Herein, we report the genetic engineering of such a docking domain complex by replacement of specific helical segments and analysis of triketide synthesis by mutant PKSs in vivo. The results of these helix swaps are fully consistent with the model and highlight residues in the docking domains that may be targeted to alter the efficiency or specificity of subunit,subunit docking in hybrid PKSs. [source]

Influence of the hydrophilic face on the folding ability and stability of ,-helix bundles: relevance to the peptide catalytic activity

CHEMICAL BIOLOGY & DRUG DESIGN, Issue 3 2000
S.E. Blondelle
Although not the sole feature responsible, the packing of amino acid side chains in the interior of proteins is known to contribute to protein conformational specificity. While a number of amphipathic peptide sequences with optimized hydrophobic domains has been designed to fold into a desired aggregation state, the contribution of the amino acids located on the hydrophilic side of such peptides to the final packing has not been investigated thoroughly. A set of self-aggregating 18-mer peptides designed previously to adopt a high level of ,-helical conformation in benign buffer is used here to evaluate the effect of the nature of the amino acids located on the hydrophilic face on the packing of a four ,-helical bundle. These peptides differ from one another by only one to four amino acid mutations on the hydrophilic face of the helix and share the same hydrophobic core. The secondary and tertiary structures in the presence or absence of denaturants were determined by circular dichroism in the far- and near-UV regions, fluorescence and nuclear magnetic resonance spectroscopy. Significant differences in folding ability, as well as chemical and thermal stabilities, were found between the peptides studied. In particular, surface salt bridges may form which would increase both the stability and extent of the tertiary structure of the peptides. The structural behavior of the peptides may be related to their ability to catalyze the decarboxylation of oxaloacetate, with peptides that have a well-defined tertiary structure acting as true catalysts. [source]