Candidate cell and matrix interaction domains on the collagen fibril, the predominant protein of vertebrates

Type I collagen, the predominant protein of vertebrates, polymerizes with type III and V collagens and non-collagenous molecules into large cable-like fibrils, yet how the fibril interacts with cells and other binding partners remains poorly understood. To help reveal insights into the collagen structure-function relationship, a data base was assembled including hundreds of type I collagen ligand binding sites and mutations on a two-dimensional model of the fibril. Visual examination of the distribution of functional sites, and statistical analysis of mutation distributions on the fibril suggest it is organized into two domains. The "cell interaction domain" is proposed to regulate dynamic aspects of collagen biology, including integrin-mediated cell interactions and fibril remodeling. The "matrix interaction domain" may assume a structural role, mediating collagen cross-linking, proteoglycan interactions, and tissue mineralization. Molecular modeling was used to superimpose the positions of functional sites and mutations from the two-dimensional fibril map onto a three-dimensional x-ray diffraction structure of the collagen microfibril in situ, indicating the existence of domains in the native fibril. Sequence searches revealed that major fibril domain elements are conserved in type I collagens through evolution and in the type II/XI collagen fibril predominant in cartilage. Moreover, the fibril domain model provides potential insights into the genotype-phenotype relationship for several classes of human connective tissue diseases, mechanisms of integrin clustering by fibrils, the polarity of fibril assembly, heterotypic fibril function, and connective tissue pathology in diabetes and aging.     

Insights into cytochrome c-cardiolipin interaction. Role played by ionic strength

The finding that cytochrome c (cyt c) plays a role in programmed cell death after its release from the mitochondrion has recently renewed interest in this protein. The structural changes in cytochrome c observed at early stages of the apoptotic process have been related to changes occurring in the protein when it forms a complex with phospholipid vesicles. Among the lipids constituting the membrane, cardiolipin is the one thought to bind to cyt c. In this paper, we have investigated the influence exerted by ionic strength on cytochrome c-cardiolipin interaction and found that formation of the cytochrome c-cardiolipin complex occurs via two distinct transitions, implying a high-affinity site and a low-affinity site. Ionic strength significantly influences complex stability; sodium chloride dissociates the complex through two distinct transitions, the second of which occurs at a very high anion concentration. ATP also dissociates the complex, but under the conditions that were investigated, its action is limited to the high-affinity site. The dissociation process is characterized by a very slow kinetic rate constant ( k obs = 4.2 x 10 (-3) s (-1)) and requires several minutes to be completed. We ascribe it to the high activation barrier met by the protein when restoring the native Fe(III)-M80 axial bond. The peroxidase activity shown by cardiolipin-bound cytochrome c is indicative of a less packed protein tertiary conformation in the complex. In line with earlier reports, these data highlight the manifold functions of cytochrome c besides the well-known role it plays in oxidative phosphorylation, shedding more light on the properties of the cytochrome c-cardiolipin complex, involved in the progression of early stages of apoptosis.     

Candida albicans cell wall comprises a branched beta-D-(1-->6)-glucan with beta-D-(1-->3)-side chains

The structure of immunogenic and immunomodulatory cell wall glucans of Candida albicans is commonly interpreted in terms of a basic polysaccharide consisting of a beta-D-(1-->3)-linked glucopyranosyl backbone possessing beta-D-(1-->6)-linked side chains of varying distribution and length. This proposed molecular architecture has been re-evaluated by the present study on the products of selective enzymolysis of insoluble C. albicans glucan particles (GG). High resolution 1H (400 and 700 MHz) and 13C (100 and 175 MHz) NMR analyses were performed on a soluble beta-glucan preparation (GG-Zym) obtained by GG digestion with endo-beta-D-(1-->3)-glucanase and on its high- (Pool 1) and low-molecular weight (Pool 2) sub-fractions. The resonances typical of uniformly beta-D-(1-->6)- and beta-D-(1-->3)-linked linear glucans, together with additional multiplets assigned to short-chain oligoglucosides, were detected in GG-Zym. Pool 1 (46.3+/-6.4% of GG-Zym content) consisted of beta-D-(1-->6)-linked glucopyranosyl polymers, with short beta-D-(1-->3)-branched side chains of 2.20+/-0.02 units (branching degree (DB)=0.14+/-0.03). Pool 2 was a mixture of glucose and linear short-chain beta-D-(1-->3)-oligoglucosides. Further digestion of Pool 1 by beta-D-(1-->6)-glucanase yielded a mixture of glucose and short beta-D-(1-->6)-linked, either linear or beta-D-(1-->3,6) branched, oligomers. These endoglucanase digestion patterns were consistent with the presence in C. albicans cell wall glucans of beta-D-(1-->6)-linked glucopyranosyl backbones possessing beta-D-(1-->3)-linked side chains, a structure very close to that of beta-D-(1-->6)-glucan from Saccharomyces cerevisiae yeast. This finding may provide the grounds for further elucidation of the cell wall structure and a better understanding of the biological properties of C. albicans beta-glucans.     

Immunomodulatory mechanisms during Echinococcus granulosus infection

The pathologic events that ensue after humans ingest the eggs of Echinococcus granulosus and continue while cystic echinococcosis develops, provide an excellent example illustrating the evasive strategies helminth parasites use to develop, progress and cause chronic disease. The hydatid cyst secretes and exposes numerous immunomodulatory molecules to the host’s immune system. By characterizing these molecules we can understand the mechanisms that E. granulosus uses for increasing the efficiency and persistency of infection in the host. These molecules modulate both the innate and adaptive arms of the immune response and appear to target cellular and humoral responses. In this review, we discuss recent advances in the immunobiology of host-E. granulosus interactions that provide intriguing insights into the complex interplay between host and parasite that ultimately facilitates parasite survival.     

In vitro perturbation of aggregation processes in beta-amyloid peptides: a spectroscopic study

We have performed an in vitro study to investigate the molecular basis of the aggregation kinetic of 1-40 beta-amyloid peptides (Abeta and the possibility of affecting this aggregation process using an exogenous natural polycyclic pigment, hypericin (Hyp). The effect of Hyp on the self-assembly process at different times of the aggregation kinetic has been investigated utilizing a chaperon-like molecule, alpha-crystallin. Circular dichroism and fluorescence results suggest that Hyp can associate to precursors of the mature fibrils and perturb the aggregation process through intermolecular interactions with the Abeta peptides.     

A thermodynamic switch for chromosome colocalization

A general model for the early recognition and colocalization of homologous DNA sequences is proposed. We show, on thermodynamic grounds, how the distance between two homologous DNA sequences is spontaneously regulated by the concentration and affinity of diffusible mediators binding them, which act as a switch between two phases corresponding to independence or colocalization of pairing regions.     

Tyramine oxidation by copper/TPQ amine oxidase and peroxidase from Euphorbia characias latex

Tyramine, an important plant intermediate, was found to be a substrate for two proteins, a copper amine oxidase and a peroxidase from Euphorbia characias latex. The oxidation of tyramine took place by two different mechanisms: oxidative deamination to p-hydroxyphenylacetaldehyde by the amine oxidase and formation of di-tyramine by the peroxidase. The di-tyramine was further oxidized at the two amino groups by the amino oxidase, whereas p-hydroxyphenylacetaldehyde was transformed to di-p-hydroxyphenylacetaldehyde by the peroxidase. Data obtained in this study indicate a new interesting scenario in the metabolism of tyramine.     

Modulation of neuropeptide Y and Y1 receptor expression in the amygdala by fluctuations in the brain content of neuroactive steroids during ethanol drinking discontinuation in Y1R/LacZ transgenic mice

Previous studies have shown that GABAergic neuroactive steroids increase Y₁ receptor (Y₁R) gene expression in the amygdala of Y ₁ R / LacZ transgenic mice, harbouring the murine Y₁R gene promoter linked to a LacZ reporter gene. As ethanol is known to increase GABAergic neuroactive steroids, we investigated the relationship between fluctuations in the brain content of neuroactive steroids induced by chronic voluntary ethanol consumption or ethanol discontinuation and both the level of neuropeptide Y (NPY) immunoreactivity and Y₁R gene expression in the amygdala of Y ₁ R / LacZ transgenic mice. Ethanol discontinuation (48 h) after voluntary consumption of consecutive solutions of 3%, 6%, 10% and 20% (v/v) ethanol over 4 weeks produced an anxiety-like behaviour as measured by elevated plus maze. Voluntary ethanol intake increased the cerebrocortical concentration of the progesterone metabolite 3α-hydroxy-5α-pregnan-20-one (3α,5α-TH PROG) that returned to control level 48 h after discontinuation of ethanol intake. Ethanol discontinuation significantly decreased NPY immunoreactivity and concomitantly increased Y ₁ R / LacZ transgene expression in the amygdala, whereas chronic ethanol intake failed to affect these parameters. The 5α-reductase inhibitor finasteride prevented both the increase in the cerebrocortical concentration of 3α,5α-TH PROG apparent after 4 weeks of ethanol intake and the changes in NPY immunoreactivity and transgene expression induced by ethanol discontinuation. Data suggest that 3α,5α-TH PROG plays an important role in the changes in NPY–Y₁R signalling in the amygdala during ethanol discontinuation.     

COOLIA CANARIENSIS SP. NOV. (DINOPHYCEAE), A NEW NONTOXIC EPIPHYTIC BENTHIC DINOFLAGELLATE FROM THE CANARY ISLANDS1

A new photosynthetic dinoflagellate species, Coolia canariensis S. Fraga sp. nov., is described based on samples taken from tidal ponds on the rocky shore of the Canary Islands, northeast Atlantic Ocean. Its morphology was studied by LM and SEM. It is almost spherical and has a thick smooth theca with many scattered pores. Plate 1′ is the biggest of the epithecal plates, and 7″ is twice as wide as it is long. Phylogeny inferred from the D1/D2 regions of the LSU nuclear rDNA of three strains of C. canariensis and several strains of other Coolia species, C. monotis, C. sp., showed that C. canariensis strains clustered in a well‐supported clade distinct from the other species. No toxins were detected using mouse bioassay, liquid chromatography with Fluorescence detection (LC‐FLD) or liquid chromatography‐mass spectrometry (LC‐MS). Its pigment composition is of the peridinin type of dinoflagellates. Together with this new species, many other strains of C. monotis from the Atlantic Ocean and Mediterranean Sea have been analyzed for toxin presence, and no evidence of toxin production related to yessotoxins (YTXs) was found, as was previously suggested for C. monotis from Australia.