Biomedical subjects

R P Vieira

Publications and source records attributed to R P Vieira.

9 recordsLinked to original sources

PubMed1997

The structures of polysaccharides and glycolipids of Aspergillus fumigatus grown in the presence of human serum.

A study was made of polysaccharides and glycosphingolipids isolated from Aspergillus fumigatus grown in media supplemented with human serum from healthy donors. Fractionation of Cetavlon-precipitated polysaccharides on Sephacryl S-400 gave rise to an excluded fraction (Fraction I) with molecular weight of > 400 kDa and an included peak (Fraction II) with an average molecular weight of 30-80 kDa. Fraction I comprises about 5% of total polysaccharide and was identified as a glycogen-like molecule. Its structure was deduced from methylation data, treatment with amyloglucosidase, a red-brown coloration produced with an iodine solution and by 1H and 13C-NMR spectroscopy. It was previously suggested that higher amounts of glycogen-like polysaccharide (20%) were present in A. fumigatus grown in serum-free medium. Fraction II was identified as a galactomannan and was the main polysaccharide of A. fumigatus grown in serum-free medium. Fraction II was identified as a galactomannan and was the main 13C-NMR spectroscopy combined with partial acetolysis and methylation analysis. The 13C-NMR spectrum of the galactomannan showed a much greater complexity in the beta-D-gal f and alpha-D-man p C-1 regions, than was evident for galactomannan from serum-free cultures previously described, reflecting differences in the glycosylation pattern, stimulated in serum-supplemented medium. No differences in A. fumigatus glycosphingolipid could be detected between serum-containing and serum-free growth conditions. Our results demonstrate that the change in polysaccharide structure is a more specific response to the altered growth conditions and not merely a symptom of more general changes.

Aspergillus fumigatus↗

PubMed1994

Sulfated fucans from echinoderms have a regular tetrasaccharide repeating unit defined by specific patterns of sulfation at the 0-2 and 0-4 positions.

Sulfated fucans from echinoderms (sea cucumber and sea urchin) have a linear backbone of 1-->3-linked alpha-L-fucopyranose with some sulfate substitution at the 2- and 4-positions. NMR spectroscopy indicates that both polysaccharides have a tetrasaccharide repeat unit in which the separate residues differ only in the extent and position of their sulfate substitution. The sea urchin fucan has the structure, [formula: see text] This type of regular structure has not previously been described, and is in contrast with the random arrangement of substituents on the similar 1-->3-linked alpha-L-fucopyranose backbone of the fucoidans from brown algae.

Animals↗

PubMed1994

Increased calcium affinity of a fucosylated chondroitin sulfate from sea cucumber.

Calcium binding and charge distribution on a fucosylated chondroitin sulfate and a standard chondroitin 6-sulfate have been studied using a metallochromic indicator and conductimetric titrations. The fucosylated chondroitin sulfate has a approximately 5-fold greater affinity for calcium ions than the standard chondroitin 6-sulfate. Possibly, this increased affinity for calcium ions is due to the branches on the fucosylated chondroitin sulfate, since the calcium affinity of an unbranched, sulfated fucan is similar to that of the standard chondroitin 6-sulfate. More charged groups per disaccharide unit (and a shorter distance between these groups) also distinguish the fucosylated chondroitin sulfate from standard chondroitin 6-sulfate. Comparison between native and chemically modified (desulfated or carboxyl-reduced) polysaccharides suggests that the sulfate esters are responsible for the increased charge density of the fucosylated chondroitin sulfate and that the presence of the fucose branches does not alter the length of the repetitive units which compose the central core of chondroitin from sea cucumber. These results are consistent with the chemical studies of these two polysaccharides.

Animals↗

PubMed1994

A sulfated alpha-L-fucan from sea cucumber.

A purified sulfated alpha-L-fucan from the sea cucumber body wall was studied, before and after almost complete desulfation, using methylation analysis and NMR spectroscopy. NMR analysis indicates that 2,4-di-O-sulfo-L-fucopyranose and unsubstituted fucopyranose are present in equal proportions, and that 2-O-sulfo-L-fucopyranose is present in twice that proportion. There is some NMR evidence that a regular repeating sequence of four residues comprises most or all of the polysaccharide chain.

Animals↗

PubMed1994

Structural analysis of sulfated fucans by high-field NMR.

The structures of several sulfated polysaccharides isolated from marine organisms have been determined by a combination of degradative and spectroscopic techniques. For two sulphated fucans, one isolated from the sea cucumber L. grisea, and one from the sea urchin L. variegatus, a novel type of polysaccharide structure is proposed based on the analysis of one- and two-dimensional nuclear magnetic resonance (NMR) spectra. Both polysaccharides are linear, 1-->3 linked alpha-L-fucans in which a four-residue repeating unit is defined by specific patterns of sulfation at the 2- and 4-positions. The four residues give rise to spin systems which may be identified by 2-dimensional 1H-1H correlated spectroscopy (COSY), and the sequence of the residues is deduced from inter-residue nuclear Overhauser enhancements which produce cross-peaks in the NOESY spectrum. To the best of our knowledge, these are the first polysaccharides for which a regular repeating unit is defined by the pattern of sulfate substitution alone.

Animals↗

PubMed1993

Extensive heterogeneity of proteoglycans bearing fucose-branched chondroitin sulfate extracted from the connective tissue of sea cucumber.

The major sulfated polysaccharide in the sea cucumber body wall is a fucose-branched chondroitin sulfate. This glycosaminoglycan has side-chain disaccharide units of sulfated fucopyranosyl or sulfate esters linked to the O-3 position of the beta-D-glucuronic acid residues. These unusual fucose branches and sulfate esters block the access of chondroitinases to the chondroitin sulfate core [Vieira & Mourão (1988) J. Biol. Chem. 263, 18176-18183; Vieira et al. (1991) J. Biol. Chem. 266, 13530-13536]. We now report the isolation and preliminary characterization of the proteoglycans bearing this unique fucose-branched chondroitin sulfate. They were extracted using guanidine hydrochloride solutions containing protease inhibitors and were purified by anion-exchange and gel-filtration columns. Interestingly, the sea cucumber proteoglycans were cleaved by chondroitinase AC or ABC, indicating that the beta-D-glucuronic acid residues close to the reducing end of the polysaccharide chain are neither fucosylated nor sulfated. SDS-polyacrylamide gel electrophoresis revealed several fractions of proteoglycans of different molecular sizes but containing a similar hexuronic acid/protein ratio and a similar type of glycan chain. Possibly, the low-molecular-size fractions arise from a protease cleavage of a larger molecule. In contrast with the results observed for most vertebrate proteoglycans, which contain a single core protein for each type of proteoglycan, chondroitinase AC or ABC releases from the sea cucumber proteoglycans a wide variety of core proteins. These observations are the first detailed study of a proteoglycan from invertebrate tissue and reveal extensive heterogeneity when compared with proteoglycans from vertebrate connective tissue.

Animals↗

PubMed1992

Experimental infection of pregnant gilts with Leptospira interrogans serovar mozdok.

Three pregnant gilts were experimentally infected with leptospires of the serovar mozdok, isolated from an aborted pig fetus from a Portuguese pig farm with abortion problems. All the gilts aborted dead or dying piglets on days 105 or 106 of pregnancy. Serovar mozdok was isolated from 12 of the 22 piglets in the three litters. Histological examination of the livers and kidneys of the gilts at the end of the experiment revealed evidence of disease, and leptospires were isolated from their kidneys. Their serological responses up to 42 days after inoculation were monitored by means of a microscopic agglutination test, using 21 antigens from 18 serogroups. Cross reactions to heterologous antigens belonging to the Grippotyphosa, Australis, Icterohaemorrhagiae and Cynopteri groups were observed in all of them.

Abortion, Veterinary↗

PubMed1991

Structure of a fucose-branched chondroitin sulfate from sea cucumber. Evidence for the presence of 3-O-sulfo-beta-D-glucuronosyl residues.

The structure of a unique focose-branched chondroitin sulfate isolated from the body wall of a sea cucumber was examined in detail. This glycosaminoglycan contains side chain disaccharide units of sulfated fucopyranosyl units linked to approximately one-half of the glucuronic acid moieties through the O-3 position of the acid. The intact polysaccharide is totally resistant to chondroitinase degradation, whereas, after defucosylation, it is partially degraded by the enzyme. However, only after an additional step of desulfation, the chondroitin from sea cucumber is almost totally degraded by chondroitinase AC or ABC. This result, together with the methylation and NMR studies of the native and chemically modified polysaccharide, suggest that besides the fucose branches, the sea cucumber chondroitin sulfate contains sulfate esters at position O-3 of the beta-D-glucuronic acid units. Furthermore, the proteoglycan from the sea cucumber chondroitin sulfate is recognized by anti-Leu-7 monoclonal antibody, which specifically recognizes 3-sulfoglucuronic acid residues. In analogy with the fucose branched units, the 3-O-sulfo-beta-D-glucuronosyl residues are resistant to chondroitinase degradation. Regarding the position of the glycosidic linkage and site of sulfation in the fucose branches, our results suggest high heterogeneity. Tentatively, it is possible to suggest the preponderance of disaccharide units formed by 3,4-di-O-sulfo-alpha-L-fucopyranosyl units glycosidically linked through position 1----2 to 4-O-sulfo-alpha-L-fucopyranose. Finally, the presence of unusual 4/6-disulfated disaccharide units, together with the common 6-sulfated and non-sulfated units, was detected in the chondroitin sulfate core of this polysaccharide.

Animals↗

PubMed1988

Occurrence of a unique fucose-branched chondroitin sulfate in the body wall of a sea cucumber.

The sulfated polysaccharides in the body wall of the sea cucumber occur as three fractions that differ markedly in molecular mass and chemical composition. The fraction containing a high molecular mass component has a high proportion of fucose and small amounts of galactose and amino sugars, whereas another fraction contains primarily a sulfated fucan. The third fraction (F-2), which represents the major portion of the sea cucumber-sulfated polysaccharides, contains approximately equimolar quantities of glucuronic acid, N-acetyl galactosamine, and fucose, and has a sulfate content higher than that in the other two fractions. The structure of fraction F-2 was examined in detail. This polysaccharide has an unusual structure composed of a chondroitin sulfate-like core, containing side chain disaccharide units of sulfated fucopyranosyl linked to approximately half of the glucuronic acid moieties through the O-3 position of the acid. These unusual fucose branches obstruct the access of chondroitinases to the chondroitin sulfate core of F-2. However, after partial acid hydrolysis, which removes the sulfated fucose residues from the polymer, fraction F-2 is degraded by chondroitinases into 6-sulfated and nonsulfated disaccharides.

Animals↗