Dissecting Carotenoid from Structural Components of Carotenoid-Based Coloration: A Field Experiment with Great Tits (Parus major)

Carotenoid-based yellowish to red plumage colors are widespread visual signals used in sexual and social communication. To understand their ultimate signaling functions, it is important to identify the proximate mechanism promoting variation in coloration. Carotenoid-based colors combine structural and pigmentary components, but the importance of the contribution of structural components to variation in pigment-based colors (i.e., carotenoid-based colors) has been undervalued. In a field experiment with great tits (Parus major), we combined a brood size manipulation with a simultaneous carotenoid supplementation in order to disentangle the effects of carotenoid availability and early growth condition on different components of the yellow breast feathers. By defining independent measures of feather carotenoid content (absolute carotenoid chroma) and background structure (background reflectance), we demonstrate that environmental factors experienced during the nestling period, namely, early growth conditions and carotenoid availability, contribute independently to variation in yellow plumage coloration. While early growth conditions affected the background reflectance of the plumage, the availability of carotenoids affected the absolute carotenoid chroma, the peak of maximum ultraviolet reflectance, and the overall shape, that is, chromatic information of the reflectance curves. These findings demonstrate that environment-induced variation in background structure contributes significantly to intraspecific variation in yellow carotenoid-based plumage coloration.

Fic domain-catalyzed adenylylation: insight provided by the structural analysis of the type IV secretion system effector BepA

Numerous bacterial pathogens subvert cellular functions of eukaryotic host cells by the injection of effector proteins via dedicated secretion systems. The type IV secretion system (T4SS) effector protein BepA from Bartonella henselae is composed of an N-terminal Fic domain and a C-terminal Bartonella intracellular delivery domain, the latter being responsible for T4SS-mediated translocation into host cells. A proteolysis resistant fragment (residues 10-302) that includes the Fic domain shows autoadenylylation activity and adenylyl transfer onto Hela cell extract proteins as demonstrated by autoradiography on incubation with α-[(32)P]-ATP. Its crystal structure, determined to 2.9-Å resolution by the SeMet-SAD method, exhibits the canonical Fic fold including the HPFxxGNGRxxR signature motif with several elaborations in loop regions and an additional β-rich domain at the C-terminus. On crystal soaking with ATP/Mg(2+), additional electron density indicated the presence of a PP(i) /Mg(2+) moiety, the side product of the adenylylation reaction, in the anion binding nest of the signature motif. On the basis of this information and that of the recent structure of IbpA(Fic2) in complex with the eukaryotic target protein Cdc42, we present a detailed model for the ternary complex of Fic with the two substrates, ATP/Mg(2+) and target tyrosine. The model is consistent with an in-line nucleophilic attack of the deprotonated side-chain hydroxyl group onto the α-phosphorus of the nucleotide to accomplish AMP transfer. Furthermore, a general, sequence-independent mechanism of target positioning through antiparallel β-strand interactions between enzyme and target is suggested.

Structural modification of DNA--a therapeutic option in SLE?

Systemic lupus erythematosus (SLE) is an autoimmune disease that affects multiple organs, with glomerulonephritis representing a frequent and serious manifestation. SLE is characterized by the presence of various autoantibodies, including anti-DNA antibodies that occur in approximately 70% of patients with SLE and which contribute to disease pathogenesis. Consequently, immunosuppressive therapies are applied in the treatment of SLE to reduce autoantibody levels. However, increasing evidence suggests that DNA--especially double--stranded DNA-constitutes an important pathogenic factor that is able to activate inflammatory responses by itself in autoimmune diseases. Therefore, modifying the structure of DNA to reduce its pathogenicity might be a more targeted approach for the treatment of SLE than immunosuppression. This article presents information in support of this strategy, and discusses the potential methods of DNA structure manipulation--in light of data obtained from mouse models of SLE--including topoisomerase I inhibition, administration of DNase I, or modification of histones using heparin or histone deacetylase inhibitors.

Structural aspects of redox-mediated electron tunneling (Dedicated to the memory of professor Alexander M. Kuznetsov)

We investigated structural aspects of electron transfer (ET) in tunneling junctions (Au(1 1 1)vertical bar FcN vertical bar solution gap vertical bar Au STM tip) with four different redox-active N-thioalk(ano)ylferrocenes (FcN) embedded. The investigated molecules consist of a redox-active ferrocene (Fc) moiety connected via alkyl spacers with N = 4, 6, 8 and 11 carbon atoms to a thiol anchoring group. We found that for short FcNs (N = 4, 6,8) the redox-mediated ET response increases with the increase of the alkyl chain length, while no enhancement of the ET was observed for Fc1 1. The model of two-step ET with partial vibrational relaxation by Kuznetsov and Ulstrup was used to rationalize these results. The theoretical ET steps were assigned to two processes: (1) electron tunneling from the Fc group to the Au tip through the electrolyte layer and (2) electron transport from the Au(1 1 1) substrate to the Fc group through the organic adlayer. We argue that for the three short FcNs, the first process represents the rate-limiting step. The increase of the length of the alkyl chain leads to an approach of the Fc group to the STM tip, and consequently accelerates the first El' step. In case of the Fcl 1 junctions the rather high thickness of the organic layer leads to a decrease of the rate of the second ET step. In consequence, the contribution of the redox-mediated current enhancement to the total tunneling current appears to be insignificant. Our work demonstrates the importance of combined structural and transport approaches for the understanding of Er processes in electrochemical nanosystems. (C) 2010 Elsevier B.V. All rights reserved.

[Influence of chronic, structural changes of the muscle-tendon unit on the indication and technique of rotator cuff reconstruction]

Rotator cuff lesions are common and the incidence increases with age. After tendon rupture of the rotator cuff, the muscle-tendon unit retracts, which is accompanied by muscle fatty infiltration, atrophy, and interstitial fibrosis of the musculature, thus, fundamentally changing the muscle architecture. These changes are important prognostic factors for the operative rotator cuff reconstruction outcome. Selection of the correct time point for reconstruction as well as the optimal mechanical fixation technique are decisive for successful attachment at the tendon-to-bone insertion site. Thus, knowledge of the pathophysiological processes plays an important role. The goal of this article is to establish a relationship between currently existing evidence with respect to the preoperatively existing changes of the muscle-tendon unit and the choice of the time for the operation and the operative technique.

Structural plasticity of hippocampal mossy fiber synapses as revealed by high-pressure freezing

Despite recent progress in fluorescence microscopy techniques, electron microscopy (EM) is still superior in the simultaneous analysis of all tissue components at high resolution. However, it is unclear to what extent conventional fixation for EM using aldehydes results in tissue alteration. Here we made an attempt to minimize tissue alteration by using rapid high-pressure freezing (HPF) of hippocampal slice cultures. We used this approach to monitor fine-structural changes at hippocampal mossy fiber synapses associated with chemically induced long-term potentiation (LTP). Synaptic plasticity in LTP has been known to involve structural changes at synapses including reorganization of the actin cytoskeleton and de novo formation of spines. While LTP-induced formation and growth of postsynaptic spines have been reported, little is known about associated structural changes in presynaptic boutons. Mossy fiber synapses are assumed to exhibit presynaptic LTP expression and are easily identified by EM. In slice cultures from wildtype mice, we found that chemical LTP increased the length of the presynaptic membrane of mossy fiber boutons, associated with a de novo formation of small spines and an increase in the number of active zones. Of note, these changes were not observed in slice cultures from Munc13-1 knockout mutants exhibiting defective vesicle priming. These findings show that activation of hippocampal mossy fibers induces pre- and postsynaptic structural changes at mossy fiber synapses that can be monitored by EM.

Structural Analysis of alpha-Fetoprotein (AFP)-like Peptides with Anti-Breast-Cancer Properties

The abundance of alpha-fetoprotein (AFP), a natural protein produced by the fetal yolk sac during pregnancy, correlates with lower incidence of estrogen receptor positive (ER+) breast cancer. The pharmacophore region of AFP has been narrowed down to a four amino acid (AA) region in the third domain of the 591 AA peptide. Our computational study focuses on a 4-mer segment consisting of the amino acids threonine-proline-valine-asparagine (TPVN). We have run replica exchange molecular dynamics (REMD) simulations and used 120 configurational snapshots from the total trajectory as starting configurations for quantum chemical calculations. We optimized structures using semiempirical (PM3, PM6, PM6-D2, PM6-H2, PM6-DH+, PM6-DH2) and density functional methods (TPSS, PBE0, M06-2X). By comparing the accuracy of these methods against RI-MP2 benchmarks, we devised a protocol for calculating the lowest energy conformers of these peptides accurately and efficiently. This protocol screens out high-energy conformers using lower levels of theory and outlines a general method for predicting small peptide structures.