A trimeric coiled-coil motif binds bacterial lipopolysaccharides with picomolar affinity.

α-helical coiled-coils are ubiquitous protein structures in all living organisms. For decades, modified coiled-coils sequences have been used in biotechnology, vaccine development, and biochemical research to induce protein oligomerization, and form self-assembled protein scaffolds. A prominent model for the versatility of coiled-coil sequences is a peptide derived from the yeast transcription factor, GCN4.

The SH3 domains of the protein kinases ITK and LCK compete for adjacent sites on T cell-specific adapter protein.

T-cell activation requires stimulation of specific intracellular signaling pathways in which protein-tyrosine kinases, phosphatases, and adapter proteins interact to transmit signals from the T-cell receptor to the nucleus. Interactions of LCK proto-oncogene, SRC family tyrosine kinase (LCK), and the IL-2-inducible T cell kinase (ITK) with the T cell-specific adapter protein (TSAD) promotes LCK-mediated phosphorylation and thereby ITK activation. Both ITK and LCK interact with TSAD's proline-rich region (PRR) through their Src homology 3 (SH3) domains.

NMR structures and mutational analysis of the two peptides constituting the bacteriocin plantaricin S.

The structure of the individual peptides of the two-peptide bacteriocin plantaricin S, an antimicrobial peptide produced by a Lactobacillus plantarum strain, has been determined in DPC micelles. The two peptides of plantaricin S, Pls-α and Pls-β, form an α-helix from and including residue 8 to 24 with a less structured region around residue 16-19 and an amphiphilic α-helix from and including residue 7 to 23, respectively. Activity assays on single amino acid-substituted GxxxG and GxxxG-like motifs show that substituting the Ser and Gly residues in the GxxxG motif in Pls-α and the SxxxG motif in Pls-β reduced or drastically reduced the antimicrobial activity.

The Leaderless Bacteriocin Enterocin K1 Is Highly Potent against : A Study on Structure, Target Spectrum and Receptor.

Enterocin K1 (EntK1), enterocin EJ97 (EntEJ97), and LsbB are three sequence related leaderless bacteriocins. Yet LsbB kills only lactococci while EntK1 and EntEJ97 target wider spectra with EntK1 being particularly active against , including nosocomial multidrug resistant isolates. NMR study of EntK1 showed that it had a structure very similar to LsbB - both having an amphiphilic N-terminal α-helix and an unstructured C-terminus.

H, C, N backbone assignment of the human heat-labile enterotoxin B-pentamer and chemical shift mapping of neolactotetraose binding.

The major virulence factor of enterotoxigenic Escherichia coli is the heat-labile enterotoxin (LT), an AB toxin closely related to the cholera toxin. LT consists of six subunits, the catalytically active A-subunit and five B-subunits arranged as a pentameric ring (LTB), which enable the toxin to bind to the epithelial cells in the intestinal lumen. LTB has two recognized binding sites; the primary binding site is responsible for anchoring the toxin to its main receptor, the GM-ganglioside, while the secondary binding site recognizes blood group antigens.

Nuclear Magnetic Resonance Structure and Mutational Analysis of the Lactococcin A Immunity Protein.

The class IId bacteriocin lactococcin A and the pediocin-like bacteriocins induce membrane leakage and cell death by specifically binding the mannose phophotransferase system (man-PTS) on their target cells. The bacteriocins' cognate immunity proteins that protect the producer cell from its own bacteriocin recognize and bind to the bacteriocin-man-PTS complex and thereby block membrane leakage. In this study, we have determined the three-dimensional structure of the lactococcin A immunity protein (LciA) by the use of nuclear magnetic resonance spectroscopy.

Structure-Function Analysis of the Two-Peptide Bacteriocin Plantaricin EF.

Plantaricin EF is a two-peptide bacteriocin that depends on the complementary action of two different peptides (PlnE and PlnF) to function. The structures of the individual peptides have previously been analyzed by nuclear magnetic resonance spectroscopy ( Fimland, N. et al.

Selective membrane disruption by the cyclotide kalata B7: complex ions and essential functional groups in the phosphatidylethanolamine binding pocket.

The cyclic cystine knot plant peptides called cyclotides are active against a wide variety of organisms. This is primarily achieved through membrane binding and disruption, in part deriving from a high affinity for phosphatidylethanolamine (PE) lipids. Some cyclotides, such as kalata B7 (kB7), form complexes with divalent cations in a pocket associated with the tyrosine residue at position 15 (Tyr15).

Interactions of a class IIb bacteriocin with a model lipid bilayer, investigated through molecular dynamics simulations.

The emergence of antibiotic resistant microorganisms poses an alarming threat to global health. Antimicrobial peptides (AMPs) are considered a possible effective alternative to conventional antibiotic therapies. An understanding of the mechanism of action of AMPs is needed in order to better control and optimize their bactericidal activity.

Defining the structure and receptor binding domain of the leaderless bacteriocin LsbB.

LsbB is a class II leaderless lactococcal bacteriocin of 30 amino acids. In the present work, the structure and function relationship of LsbB was assessed. Structure determination by NMR spectroscopy showed that LsbB has an N-terminal α-helix, whereas the C-terminal of the molecule remains unstructured.

The arabidopsis histone methyltransferase SUVR4 binds ubiquitin via a domain with a four-helix bundle structure.

In eukaryotes, different chromatin states facilitate or repress gene expression and restrict the activity of transposable elements. Post-translational modifications (PTMs) of amino acid residues on the N-terminal tails of histones are suggested to define such states. The histone lysine methyltransferase (HKMTase) SU(VAR)3-9 RELATED4 (SUVR4) of Arabidopsis thaliana functions as a repressor of transposon activity.

Solubility of recombinant Src homology 2 domains expressed in E. coli can be predicted by TANGO.

Background: Signalling proteins often contain several well defined and conserved protein domains. Structural analyses of such domains by nuclear magnetic spectroscopy or X-ray crystallography may greatly inform the function of proteins. A limiting step is often the production of sufficient amounts of the recombinant protein.

Effects of conserved residues and naturally occurring mutations on Mycobacterium tuberculosis RecG helicase activity.

RecG is a helicase that is conserved in nearly all bacterial species. The prototypical Escherichia coli RecG promotes regression of stalled replication forks, participates in DNA recombination and DNA repair, and prevents aberrant replication. Mycobacterium tuberculosis RecG (RecGMtb) is a DNA-dependent ATPase that unwinds a variety of DNA substrates, although its preferred substrate is a Holliday junction.

Mapping of the immunodominant regions of shrimp tropomyosin Pan b 1 by human IgE-binding and IgE receptor crosslinking studies.

Background: Epitope mapping of an allergen is generally done by IgE-binding assays with short synthetic peptides, but this provides little information about which domains are responsible for IgE receptor crosslinking on effector cells. Our aim was to map the immunodominant regions of shrimp tropomyosin by both IgE-binding and IgE-receptor crosslinking studies.

Methods: Five overlapping fragments covering Pandalus borealis tropomyosin were cloned, expressed in Escherichia coli and characterized by circular dichroism spectroscopy, native PAGE and bis(sulfosuccinimidyl) suberate-crosslinking.

The CW domain, a new histone recognition module in chromatin proteins.

Post-translational modifications of the N-terminal histone tails, including lysine methylation, have key roles in regulation of chromatin and gene expression. A number of protein modules have been identified that recognize differentially modified histone tails and provide their proteins with the capacity to sense such modifications. Here, we identify the CW domain of plant and animal chromatin-related proteins as a novel module that recognizes different methylated states of lysine 4 on histone H3 (H3K4me).

The antibacterial ent-eusynstyelamide B and eusynstyelamides D, E, and F from the Arctic bryozoan Tegella cf. spitzbergensis.

The brominated tryptophan-derived ent-eusynstyelamide B (1) and three new derivatives, eusynstyelamides D, E, and F (2-4), were isolated from the Arctic bryozoan Tegella cf. spitzbergensis. The structures were elucidated by spectroscopic methods including 1D and 2D NMR and analysis of mass spectrometric data.

Structure and Mode-of-Action of the Two-Peptide (Class-IIb) Bacteriocins.

This review focuses on the structure and mode-of-action of the two-peptide (class-IIb) bacteriocins that consist of two different peptides whose genes are next to each other in the same operon. Optimal antibacterial activity requires the presence of both peptides in about equal amounts. The two peptides are synthesized as preforms that contain a 15-30 residue double-glycine-type N-terminal leader sequence that is cleaved off at the C-terminal side of two glycine residues by a dedicated ABC-transporter that concomitantly transfers the bacteriocin peptides across cell membranes.

Structure analysis of the two-peptide bacteriocin lactococcin G by introducing D-amino acid residues.

The importance of 3D structuring in the N- and C-terminal ends of the two peptides (39-mer LcnG-alpha and 35-mer LcnG-beta) that constitute the two-peptide bacteriocin lactococcin G was analysed by replacing residues in the end regions with the corresponding D-isomeric residues. When assayed for antibacterial activity in combination with the complementary wild-type peptide, LcnG-alpha with four D-residues in its C-terminal region and LcnG-beta with four d-residues in either its N- or its C-terminal region were relatively active (two- to 20-fold reduction in activity). 3D structuring of the C-terminal region in LcnG-alpha and the C- and N-terminal regions in LcnG-beta is thus not particularly critical for retaining antibacterial activity, indicating that the 3D structure of these regions is not vital for interpeptide interactions or for interactions between the peptides and cellular components.

Periplasmic expression of soluble single chain T cell receptors is rescued by the chaperone FkpA.

Background: Efficient expression systems exist for antibody (Ab) molecules, which allow for characterization of large numbers of individual Ab variants. In contrast, such expression systems have been lacking for soluble T cell receptors (TCRs). Attempts to generate bacterial systems have generally resulted in low yields and material which is prone to aggregation and proteolysis.

Three-dimensional structure of the two-peptide bacteriocin plantaricin JK.

The three-dimensional structures of the two peptides, PlnJ and PlnK, that constitutes the two-peptide bacteriocin plantaricin JK have been solved in water/TFE and water/DPC-micellar solutions using nuclear magnetic resonance (NMR) spectroscopy. PlnJ, a 25 residue peptide, has an N-terminal amphiphilic alpha-helix between Trp-3 and Tyr-15. The 32 residues long PlnK forms a central amphiphilic alpha-helix between Gly-9 and Leu-24.

Identification of a high affinity FcgammaRIIA-binding peptide that distinguishes FcgammaRIIA from FcgammaRIIB and exploits FcgammaRIIA-mediated phagocytosis and degradation.

FcgammaRIIA is a key activating receptor linking immune complex formation with cellular effector functions. FcgammaRIIA has 93% identity with an inhibitory receptor, FcgammaRIIB, which negatively regulates FcgammaRIIA. FcgammaRIIA is important in the therapeutic action of several monoclonal antibodies.

Mutational analysis of the class IIa bacteriocin curvacin A and its orientation in target cell membranes.

To analyze the orientation in target cell membranes of the pediocin-like bacteriocin (antimicrobial peptide) curvacin A, 55 variants were generated by site-directed mutagenesis and their potencies against four different target cells determined. The result suggest that the somewhat hydrophilic short central helix (residues 19 to 24), along with the N-terminal beta-sheet-like structure (residues 1 to 16), inserts in the interface region of the target cell membrane, with Ala22 close to the hydrophobic core of the membrane. The following hinge region, with Gly28 as an important residue, may then form a turn wherein Gly28 becomes positioned near the border between the interface and the hydrophobic regions, thus permitting the longer and more-hydrophobic C-terminal helix (residues 29 to 41) to insert into the hydrophobic core of the membrane.

Three-dimensional structure of the two peptides that constitute the two-peptide bacteriocin plantaricin EF.

The three-dimensional structures of the two peptides plantaricin E (plnE; 33 residues) and plantaricin F (plnF; 34 residues) constituting the two-peptide bacteriocin plantaricin EF (plnEF) have been determined by nuclear magnetic resonance (NMR) spectroscopy in the presence of DPC micelles. PlnE has an N-terminal alpha-helix (residues 10-21), and a C-terminal alpha-helix-like structure (residues 25-31). PlnF has a long central alpha-helix (residues 7-32) with a kink of 38+/-7 degrees at Pro20.

Mutational analysis of putative helix-helix interacting GxxxG-motifs and tryptophan residues in the two-peptide bacteriocin lactococcin G.

The membrane-permeabilizing two-peptide bacteriocin lactococcin G consists of two different peptides, LcnG-alpha and LcnG-beta. The bacteriocin contains several tryptophan and tyrosine residues and three putative helix-helix interacting GxxxG-motifs, G 7xxxG 11 and G 18xxxG 22 in LcnG-alpha and G 18xxxG 22 in LcnG-beta. The tryptophan and tyrosine residues and residues in the GxxxG-motifs were altered by site-directed mutagenesis to analyze the structure and membrane-orientation of lactococcin G.