Evidence for the formation of covalent bonds between macromolecules in the domain of the wall of Candida albicans mycelial cells

An O-glycosylated mannoprotein, after its incorporation into the wall, showed an increase in its molecular weight, due at least to its association with N-glycosidic sugar chain(s). This was shown by rendering the material soluble after partial degradation of the wall structure. At present it is unknown whether this phenomenon is due to an additional transglycosylation process or whether the partial degradation of the wall solubilizes a supramolecular structure formed between the original O-glycosylated protein which becomes linked either directly or indirectly through a protein to the N-sugar chain(s).     

Distribution pattern of decapod larvae off the north-western Iberian Peninsula coast (NE Atlantic)

In October 1977 the model of general circulation of the watermasses off the coast of Galicia, and the presence of a coastalupwelling, led to a high primary productivity. This high productivityin turn favoured the development of a rich population of decapodlarvae. The abundance and distribution pattern of these organismswere closely linked (i) to the abundant presence of the correspondingadult species in the area, (ii) with the spatial distributionof phytoplanktonic populations concurrently studied by Estrada[J. Plankton Res ., 6, 417–434 (1984)] and (iii) withthe hydrodynamic pattern in the area. Fifty-two decapod larvaetaxa were identified and Solenocera membranacea, Pisidia longicornis,Pilumnushirtellus and Goneplax rhomboides were the most representativespecies It was observed that the greatest concentrations oflarvae (3387 larvae 10^–2 m^–3) were to be found nearthe mouth of the Rfas Baixas (situated in the south-west ofthe coastal area) and in some zones further out to sea (863larvae 10^–2 m^–3) (due to a process of hydrodynamictransport)     

Calcofluor white alters the assembly of chitin fibrils in Saccharomyces cerevisiae and Candida albicans cells

In the presence of calcofluor white, budding scars and dividing cross-walls of Saccharomyces cerevisiae exhibited fluorescence, indicating that the brightener was a specific marker of fungal chitin. In addition, incubation of cells in the presence of the brightener did not stop protein and wall-polymer formation, but abnormal deposition of chitin occurred. Chitin synthesis was normal in regenerating protoplasts of Candida albicans in the presence of calcofluor, but formation of the crystalline lattice was blocked. These results suggest that crystallization of nascent subunits may occur by a self-assembly mechanism that was blocked by the stain.     

Biosynthesis of the yeast cell wall: Selective assays and regulation of some mannosyl transferase activities

Assays have been developed for some transfer reactions involved in the synthesis of Saccharomyces cerevisiae wall mannoproteins, both in a particulate preparation in the presence of EDTA or Triton X-100, and after lipid extraction with chloroform-methanol at -20C.The mannosyl transferase activities were also studied in cells made permeable to GDP-mannose by toluene-ethanol treatment (in situ). In these permeabilized cells, the glycosylating reactions dependent on lipid carriers (dolichol derivatives) did not function, but those independent of them were unaffected.The lipid-independent mannosyl transferase activities were partially inhibited by nucleotide diphosphates probably in a competitive manner. Increase of the nucleotide diphosphate pool in vivo might slow down the speed of the transfer reactions carried out by the mannan synthetase system.     

Minor- and trace-element intra-shell variations in Santonian inoceramids (Basque-Cantabrian Basin,northern Spain): diagenetic and primary causes

Santonian deep- and platform-marine facies inoceramids from the Basque-Cantabrian Basin show clear saw-toothed intra-shell variations with respect to Mg/Ca, Sr/Ca, Na/Ca, Ba/Ca, Fe/Ca and Mn/Ca ratios. Under cathodoluminescence, the most luminescent zones in all the inoceramids present lower Mg/Ca and Sr/Ca (up to 48% and 35% lower values, respectively) and higher Fe/Ca and Mn/Ca ratios (up to 362% and 819% higher values, respectively), which is indicative of diagenetic modification. In contrast, the least luminescent zones show higher Mg/Ca and Sr/Ca ratios and lower Fe/Ca and Mn/Ca. These findings, along with the presence of frequent, well-correlated Mg/Ca, Sr/Ca and Na/Ca ratios, inversely related to Fe/Ca and Mn/Ca, in the weakest luminescent zones suggest major retention of the primary intra-shell variations in these zones. Moreover, Ba/Ca profiles, not connected with the general cathodoluminescence behaviour of the shells, also point towards partial retention of the primary patterns. The saw-toothed intra-shell variations are thought to be caused by the distinct geochemical signals acquired originally by the inoceramid alternating clear and dark growth lines. The deposition of the growth lines and thus the saw-toothed intra-shell variations may be mainly related to periodically changing palaeoenvironmental conditions, such as seawater temperature variations and phytodetritus rainfall. This interpretation is supported by the appearance of highly similar chemical saw-toothed variations in the extant shallow-marine Atrina rigida shell.     

MAPK-dependent degradation of G protein-coupled receptor kinase 2

G protein-coupled receptor kinase 2 (GRK2) is a key modulator of G protein-coupled receptors (GPCR). Altered expression of GRK2 has been described to occur during pathological conditions characterized by impaired GPCR signaling. We have reported recently that GRK2 is rapidly degraded by the proteasome pathway and that beta-arrestin function and Src-mediated phosphorylation are involved in targeting GRK2 for proteolysis. In this report, we show that phosphorylation of GRK2 by MAPK also triggers GRK2 turnover by the proteasome pathway. Modulation of MAPK activation alters the degradation of transfected or endogenous GRK2, and a GRK2 mutant that mimics phosphorylation by MAPK shows an enhanced degradation rate, thus indicating a direct effect of MAPK on GRK2 turnover. Interestingly, MAPK-mediated modulation of wild-type GRK2 stability requires beta-arrestin function and is facilitated by previous phosphorylation of GRK2 on tyrosine residues by c-Src. Consistent with an important physiological role, interfering with this GRK2 degradation process results in altered GPCR responsiveness. Our data suggest that both c-Src and MAPK-mediated phosphorylation would contribute to modulate GRK2 degradation, and put forward the existence of new feedback mechanisms connecting MAPK cascades and GPCR signaling.     

New species of benthopelagic hydromedusae from the Weddell Sea

Four medusa species were collected by an epibenthic sledge during the "Polarstern" ANT XV/3 cruise carried out from January to March 1998 in the eastern Weddell Sea. The specimens were collected in the benthic boundary layer at depths ranging between 1,583 and 2,034 m; 2 of the species collected are new to science. The narcomedusa Sigiweddellia bathypelagica gen. nov. et sp. nov. is characterised by two types of marginal tentacles and closed marginal statocysts. The trachymedusa Voragonema laciniata sp. nov. (known only from the single holotype) is characterised by the number and irregular shape of the centripetal canals. These findings are the first to report benthopelagic hydromedusae in deep Antarctic waters. Examination of several specimens of Benthocodon pedunculata (Bigelow 1913) leads us to move it to the genus Voragonema Naumov 1971 because of the clear presence of centripetal expansions in the ring canal.     

Cloning and Characterization of PRA1, a Gene Encoding a Novel pH-Regulated Antigen of Candida albicans

Candida albicans is an opportunistic fungal pathogen of humans. The cell wall of the organism defines the interface between the pathogen and host tissues and is likely to play an essential and pivotal role in the host-pathogen interaction. The components of the cell wall critical to this interaction are undefined. Immunoscreening of a lambda expression library with sera raised against mycelial cell walls of C. albicans was used to identify genes encoding cell surface proteins. One of the positive clones represented a candidal gene that was differentially expressed in response to changes in the pH of the culture medium. Maximal expression occurred at neutral pH, with no expression detected below pH 6.0. On the basis of the expression pattern, the corresponding gene was designated PRA1, for pH-regulated antigen. The protein predicted from the nucleotide sequence was 299 amino acids long with motifs characteristic of secreted glycoproteins. The predicted surface localization and N glycosylation of the protein were directly demonstrated by cell fractionation and immunoblot analysis. Deletion of the gene imparted a temperature-dependent defect in hypha formation, indicating a role in morphogenesis. The PRA1 protein was homologous to surface antigens of Aspergillus spp. which react with serum from aspergillosis patients, suggesting that the PRA1 protein may have a role in the host-parasite interaction during candidal infection.