Protein disorder: conformational distribution of the flexible linker in a chimeric double cellulase

The structural properties of the linker peptide connecting the cellulose-binding module to the catalytic module in bimodular cellulases have been investigated by small-angle x-ray scattering. Since the linker and the cellulose-binding module are relatively small and cannot be readily detected separately, the conformation of the linker was studied by means of an artificial fusion protein, Cel6BA, in which an 88-residue linker connects the large catalytic modules of the cellulases Cel6A and Cel6B from Humicola insolens. Our data showed that Cel6BA is very elongated with a maximum dimension of 178 A, but could not be described by a single conformation. Modeling of a series of Cel6BA conformers with interdomain separations ranging between 10 A and 130 A showed that good Guinier and P(r) profile fits were obtained by a weighted average of the scattering curves of all the models where the linker follows a nonrandom distribution, with a preference for the more compact conformers. These structural properties are likely to be essential for the function of the linker as a molecular spring between the two functional modules. Small-angle x-ray scattering therefore provides a unique tool to quantitatively analyze the conformational disorder typical of proteins described as natively unfolded.     

Comparative analysis of the human and chicken prion protein copper binding regions at pH 6.5

Recent experimental evidence supports the hypothesis that prion proteins (PrPs) are involved in the Cu(II) metabolism. Moreover, the copper binding region has been implicated in transmissible spongiform encephalopathies, which are caused by the infectious isoform of prion proteins (PrP(Sc)). In contrast to mammalian PrP, avian prion proteins have a considerably different N-terminal copper binding region and, most interestingly, are not able to undergo the conversion process into an infectious isoform. Therefore, we applied x-ray absorption spectroscopy to analyze in detail the Cu(II) geometry of selected synthetic human PrP Cu(II) octapeptide complexes in comparison with the corresponding chicken PrP hexapeptide complexes at pH 6.5, which mimics the conditions in the endocytic compartments of neuronal cells. Our results revealed that structure and coordination of the human PrP copper binding sites are highly conserved in the pH 6.5-7.4 range, indicating that the reported pH dependence of copper binding to PrP becomes significant at lower pH values. Furthermore, the different chicken PrP hexarepeat motifs display homologous Cu(II) coordination at sub-stoichiometric copper concentrations. Regarding the fully cation-saturated prion proteins, however, a reduced copper coordination capability is supposed for the chicken prion protein based on the observation that chicken PrP is not able to form an intra-repeat Cu(II) binding site. These results provide new insights into the prion protein structure-function relationship and the conversion process of PrP.     

The course of malaria in mice: major histocompatibility complex (MHC) effects, but no general MHC heterozygote advantage in single-strain infections

A general MHC-heterozygote advantage in parasite-infected organisms is often assumed, although there is little experimental evidence for this. We tested the response of MHC-congenic mice (F2 segregants) to malaria and found the course of infection to be significantly influenced by MHC haplotype, parasite strain, and host gender. However, the MHC heterozygotes did worse than expected from the average response of the homozygotes.     

Cross talk between MyD88 and focal adhesion kinase pathways

Focal adhesion kinase (FAK) is a nonreceptor protein tyrosine kinase involved in signaling downstream of integrins, linking bacterial detection, cell entry, and initiation of proinflammatory response through MAPKs and NF-kappaB activation. In this study, using protein I/II from Streptococcus mutans as a model activator of FAK, we investigated the potential link between FAK and TLR pathways. Using macrophages from TLR- or MyD88-deficient mice, we report that MyD88 plays a major role in FAK-dependent protein I/II-induced cytokine release. However, response to protein I/II stimulation was independent of TLR4, TLR2, and TLR6. The data suggest that there is a cross talk between FAK and MyD88 signaling pathways. Moreover, MyD88-dependent, LPS-induced IL-6 secretion by human and murine fibroblasts required the presence of FAK, confirming that MyD88 and FAK pathways are interlinked.     

Mutations in the VLGR1 gene implicate G-protein signaling in the pathogenesis of Usher syndrome type II

Usher syndrome type II (USH2) is a genetically heterogeneous autosomal recessive disorder with at least three genetic subtypes (USH2A, USH2B, and USH2C) and is classified phenotypically as congenital hearing loss and progressive retinitis pigmentosa. The VLGR1 (MASS1) gene in the 5q14.3-q21.1 USH2C locus was considered a likely candidate on the basis of its protein motif structure and expressed-sequence-tag representation from both cochlear and retinal subtracted libraries. Denaturing high-performance liquid chromatography and direct sequencing of polymerase-chain-reaction products amplified from 10 genetically independent patients with USH2C and 156 other patients with USH2 identified four isoform-specific VLGR1 mutations (Q2301X, I2906FS, M2931FS, and T6244X) from three families with USH2C, as well as two sporadic cases. All patients with VLGR1 mutations are female, a significant deviation from random expectations. The ligand(s) for the VLGR1 protein is unknown, but on the basis of its potential extracellular and intracellular protein-protein interaction domains and its wide mRNA expression profile, it is probable that VLGR1 serves diverse cellular and signaling processes. VLGR1 mutations have been previously identified in both humans and mice and are associated with a reflex-seizure phenotype in both species. The identification of additional VLGR1 mutations to test whether a phenotype/genotype correlation exists, akin to that shown for other Usher syndrome disease genes, is warranted.     

Synthetic human prion protein octapeptide repeat binds to the proteinase K active site

Proteinase K is widely used in tests for the presence of infectious prion protein causing fatal spongiform encephalopathies. To investigate possible interactions between the enzyme and the functionally important N-terminal prion domain, we crystallized mercury-inhibited proteinase K in the presence of the synthetic peptides GGGWGQPH and HGGGW. The octapeptide sequence is identical to that of a single octapeptide repeat (OPR) from the physiologically important OPR region. Here, we present the first direct evidence for the complex formation between a proteolytic enzyme and a segment of human prion molecule. The X-ray structures of the complexes at 1.4 and 1.8A resolution, respectively, revealed that in both cases the segment GGG is strongly bound as a real substrate at the substrate recognition site of the proteinase forming an antiparallel beta-strand between the two parallel strands of Asn99-Tyr104 and Ser132-Gly136. The complex is stabilized through an extended H-bonding network.     

Oceanic fronts in the Sargasso Sea control the early life and drift of Atlantic eels

Anguillid freshwater eels show remarkable life histories. In the Atlantic, the European eel (Anguilla anguilla) and American eel (Anguilla rostrata) undertake extensive migrations to spawn in the oceanic Sargasso Sea, and subsequently the offspring drift to foraging areas in Europe and North America, first as leaf-like leptocephali larvae that later metamorphose into glass eels. Since recruitment of European and American glass eels has declined drastically during past decades, there is a strong demand for further understanding of the early, oceanic phase of their life cycle. Consequently, during a field expedition to the eel spawning sites in the Sargasso Sea, we carried out a wide range of dedicated bio-physical studies across areas of eel larval distribution. Our findings suggest a key role of oceanic frontal processes, retaining eel larvae within a zone of enhanced feeding conditions and steering their drift. The majority of the more westerly distributed American eel larvae are likely to follow a westerly/northerly drift route entrained in the Antilles/Florida Currents. European eel larvae are generally believed to initially follow the same route, but their more easterly distribution close to the eastward flowing Subtropical Counter Current indicates that these larvae could follow a shorter, eastward route towards the Azores and Europe. The findings emphasize the significance of oceanic physical–biological linkages in the life-cycle completion of Atlantic eels.     

Molecular Details of Bax Activation, Oligomerization, and Membrane Insertion

Bax and Bid are pro-apoptotic members of the Bcl-2 protein family. Upon cleavage by caspase-8, Bid activates Bax. Activated Bax inserts into the mitochondrial outer membrane forming oligomers which lead to membrane poration, release of cytochrome c, and apoptosis. The detailed mechanism of Bax activation and the topology and composition of the oligomers are still under debate. Here molecular details of Bax activation and oligomerization were obtained by application of several biophysical techniques, including atomic force microscopy, cryoelectron microscopy, and particularly electron paramagnetic resonance (EPR) spectroscopy performed on spin-labeled Bax. Incubation with detergents, reconstitution, and Bid-triggered insertion into liposomes were found to be effective in inducing Bax oligomerization. Bid was shown to activate Bax independently of the stoichiometric ratio, suggesting that Bid has a catalytic function and that the interaction with Bax is transient. The formation of a stable dimerization interface involving two Bcl-2 homology 3 (BH3) domains was found to be the nucleation event for Bax homo-oligomerization. Based on intermolecular distance determined by EPR, a model of six adjacent Bax molecules in the oligomer is presented where the hydrophobic hairpins (helices α5 and α6) are equally spaced in the membrane and the two BH3 domains are in close vicinity in the dimer interface, separated by >5 nm from the next BH3 pairs.     

Wavelength-dependent effects of evening light exposure on sleep architecture and sleep EEG power density in men

Light strongly influences the circadian timing system in humans via non-image-forming photoreceptors in the retinal ganglion cells. Their spectral sensitivity is highest in the short-wavelength range of the visible light spectrum as demonstrated by melatonin suppression, circadian phase shifting, acute physiological responses, and subjective alertness. We tested the impact of short wavelength light (460 nm) on sleep EEG power spectra and sleep architecture. We hypothesized that its acute action on sleep is similar in magnitude to reported effects for polychromatic light at higher intensities and stronger than longer wavelength light (550 nm). The sleep EEGs of eight young men were analyzed after 2-h evening exposure to blue (460 nm) and green (550 nm) light of equal photon densities (2.8 x 10(13) photons x cm(-2) x s(-1)) and to dark (0 lux) under constant posture conditions. The time course of EEG slow-wave activity (SWA; 0.75-4.5 Hz) across sleep cycles after blue light at 460 nm was changed such that SWA was slightly reduced in the first and significantly increased during the third sleep cycle in parietal and occipital brain regions. Moreover, blue light significantly shortened rapid eye movement (REM) sleep duration during these two sleep cycles. Thus the light effects on the dynamics of SWA and REM sleep durations were blue shifted relative to the three-cone visual photopic system probably mediated by the circadian, non-image-forming visual system. Our results can be interpreted in terms of an induction of a circadian phase delay and/or repercussions of a stronger alerting effect after blue light, persisting into the sleep episode.