Resolution and characterization of tryptophyl fluorescence of hen egg-white lysozyme by quenching- and time-resolved spectroscopy. (9/1610)

The fluorescence spectral distributions of four tryptophan residues of hen egg-white lysozyme were analyzed using time-resolved and quenching-resolved fluorescence spectroscopy. Trp62 and Trp108 gave the fluorescence maxima at 352 nm and 342 nm, respectively. The fluorescence of Trp28 and Trp111 occurred only at 300-360 nm and they were observed as an unresolved emission band with a maximum and shoulder at 320 nm and 330 nm. The fluorescence quenching and decay parameters of each tryptophan residue reconfirmed that Trp62 was fully exposed to the solvent but Trp108 was sealed in the cage of the peptide chains and furthermore showed that Trp28 and Trp111 are under the influence of the larger fluctuational motion at the hydrophobic matrix box. The fluorescence responses of each tryptophan residue to the lysozyme-ligand interaction suggested that the internal fluctuation was reduced by the binding of ligand to give a distorted conformation to the hydrophobic matrix box region.  (+info)

Distribution of chitinase in guinea pig tissues and increases in levels of this enzyme after systemic infection with Aspergillus fumigatus. (10/1610)

Intravenous infection of guinea pigs with the fungus Aspergillus fumigatus resulted in increased levels of chitinase in serum and tissues of the animals. The molecular properties of the enzyme were demonstrated to be different from those of the fungal chitinase, but also from guinea pig lysozyme and beta-N-acetylhexosaminidase. Bio-Gel P-100 gel filtration showed that in liver, spleen, heart and lung tissue of control animals there were two molecular mass forms present with apparent molecular masses of 35 kDa and 15 kDa. In brain and serum, only the 35 kDa form was detectable. Kidney showed only the 15 kDa form. Upon infection the 35 kDa form appeared in kidney and increased in the other tissues. When a less pathogenic form of the fungus was used the 35 kDa form remained absent in kidney. In contrast to human serum chitinase, the enzyme from guinea pig serum and tissues did bind to concanavalin A-Sepharose. This was the case for both molecular mass forms. The mode of cleavage of the substrate 4-methylumbelliferyl-tri-N-acetylchitotrioside (MU-[GlcNAc]3, where GlcNAc is N-acetylglucosamine) by the two forms of the enzyme was the same: both [GlcNAc]2 and [GlcNAc]3 were released. The chitinase activity levels in the control tissues showed a large variation in this order: spleen > lung, kidney > liver > heart > brain. The fact that spleen showed the highest chitinase level is in agreement with its major role as a lymphoid organ in cases of systemic infections. The relative increases upon infection were the highest for the tissues that showed low control values.  (+info)

Cytosol-to-lysosome transport of free polymannose-type oligosaccharides. Kinetic and specificity studies using rat liver lysosomes. (11/1610)

In hepatocellular carcinoma HepG2 cells, free polymannose-type oligosaccharides appearing in the cytosol during the biosynthesis and quality control of glycoproteins are rapidly translocated into lysosomes by an as yet poorly defined process (Saint-Pol, A., Bauvy, C., Codogno, P., and Moore, S. E. H. (1997) J. Cell Biol. 136, 45-59). Here, we demonstrate an ATP-dependent association of [2-3H]mannose-labeled Man5GlcNAc with isolated rat liver lysosomes. This association was only observed in the presence of swainsonine, a mannosidase inhibitor, which was required for the protection of sedimentable, but not nonsedimentable, Man5GlcNAc from degradation, indicating that oligosaccharides were transported into lysosomes. Saturable high affinity transport (Kuptake, 22.3 microM, Vmax, 7.1 fmol/min/unit of beta-hexosaminidase) was dependent upon the hydrolysis of ATP but independent of vacuolar H+/ATPase activity. Transport was inhibited strongly by NEM and weakly by vanadate but not by sodium azide, and, in addition, the sugar transport inhibitors phloretin, phloridzin, and cytochalasin B were without effect on transport. Oligosaccharide import did not show absolute specificity but was selective toward partially demannosylated and dephosphorylated oligosaccharides, and, furthermore, inhibition studies revealed that the free reducing GlcNAc residue of the oligosaccharide was of critical importance for its interaction with the transporter. These results demonstrate the presence of a novel lysosomal free oligosaccharide transporter that must work in concert with cytosolic hydrolases in order to clear the cytosol of endoplasmic reticulum-generated free oligosaccharides.  (+info)

Tachylectin-2: crystal structure of a specific GlcNAc/GalNAc-binding lectin involved in the innate immunity host defense of the Japanese horseshoe crab Tachypleus tridentatus. (12/1610)

Tachylectin-2, isolated from large granules of the hemocytes of the Japanese horseshoe crab (Tachypleus tridentatus), is a 236 amino acid protein belonging to the lectins. It binds specifically to N-acetylglucosamine and N-acetylgalactosamine and is a part of the innate immunity host defense system of the horseshoe crab. The X-ray structure of tachylectin-2 was solved at 2.0 A resolution by the multiple isomorphous replacement method and this molecular model was employed to solve the X-ray structure of the complex with N-acetylglucosamine. Tachylectin-2 is the first protein displaying a five-bladed beta-propeller structure. Five four-stranded antiparallel beta-sheets of W-like topology are arranged around a central water-filled tunnel, with the water molecules arranged as a pentagonal dodecahedron. Tachylectin-2 exhibits five virtually identical binding sites, one in each beta-sheet. The binding sites are located between adjacent beta-sheets and are made by a large loop between the outermost strands of the beta-sheets and the connecting segment from the previous beta-sheet. The high number of five binding sites within the single polypeptide chain strongly suggests the recognition of carbohydrate surface structures of pathogens with a fairly high ligand density. Thus, tachylectin-2 employs strict specificity for certain N-acetyl sugars as well as the surface ligand density for self/non-self recognition.  (+info)

Inositol acylation of glycosylphosphatidylinositols in the pathogenic fungus Cryptococcus neoformans and the model yeast Saccharomyces cerevisiae. (13/1610)

Cryptococcus neoformans, an opportunistic fungus responsible for life-threatening infection in immunocompromised patients, is able to synthesize glycosylphosphatidylinositol (GPI) structures. Radiolabelling experiments in vitro with the use of a cryptococcal cell-free system showed that the pathway begins as in other eukaryotes, with the addition of N-acetylglucosamine to phosphatidylinositol, followed by deacetylation of the sugar residue. The third step, acylation of the inositol ring, seemed to involve a fatty acid other than palmitate, in contrast with previous findings in Saccharomyces cerevisiae and mammalian GPI pathways. A systematic study of inositol acylation in C. neoformans and S. cerevisiae showed that both organisms used a variety of fatty acids in this step; these were transferred directly from acyl-CoA to inositol without modification. However, the specificity of fatty acid utilization was quite distinct in the two fungi, with the pathogen being substantially more restrictive. In mammalian cells fatty acids added exogenously as acyl-CoAs are not transferred directly to inositol. These results suggest significant differences in the GPI biosynthetic pathway between mammalian and C. neoformans cells that could represent targets for anti-cryptococcal therapy.  (+info)

Mutant strains (nit) of Salmonella typhimurium with a pleiotropic defect in nitrogen metabolism. (14/1610)

We have isolated mutant strains (nit) of Salmonella typhimurium that are defective in nitrogen metabolism. They have a reduced ability to use a variety of compounds including glutamate, proline, arginine, N-acetyl-glucosamine, alanine, and adenosine as sole nitrogen source. In addition, although they grow normally on high concentrations of ammonium chloride (greater than 1 mM) as nitrogen source, they grow substantially more slowly than wild type at low concentrations (less than 1 mM). We postulated that the inability of these strains to utilize low concentrations of ammonium chloride accounts for their poor growth on other nitrogen sources. The specific biochemical lesion in strains with a nit mutation is not known; however, mutant strains have no detectable alteration in the activities of glutamine synthetase, glutamate synthetase, or glutamate dehydrogenase, the enzymes known to be involved in assimilation of ammonia. A nit mutation is suppressed by second-site mutations in the structural gene for glutamine synthetase (glnA) that decrease glutamine synthetase activity.  (+info)

Interactions on 3-deoxy and 6-deoxy derivatives of N-acetyl-D-glucosamine with hen lysozyme. (15/1610)

The interactions of deoxy derivatives of GlcNAc, 6-deoxy-GlcNAc, and 3-deoxy-GlcNAc with hen egg-white lysozyme [EC] were studied at various pH's by measuring the changes in the circular dichroic (CD) band at 295 nm. It was shown that 6-deoxy-GlcNAc and 3-deoxy-GlcNAc bind at subsite C of lysozyme and compete with GlcNAc. The pH dependence of the binding constant of 6-deoxy-GlcNAc was the same as that of GlcNAc. On the other hand, the binding constants of 3-deoxy-GlcNAc were 3--10 times smaller than those of GlcNAc in the pH range from 3 to 9. X-ray crystallographic studies show that O(6) and O(3) of GlcNAc at subsite C are hydrogen-bonded to the indole NH's of Trp 62 and Trp 63, respectively, but the above results indicate that Trp 63, not Trp 62, is important for the interaction of GlcNAc with lysozyme.  (+info)

Interactions of alpha- and beta-N-acetyl-D-glucosamines with hen and turkey lysozymes. (16/1610)

The binding constants of alpha- and beta-GlcNAc to hen and turkey lysozymes [EC] were determined at various pH's using the method proposed by Ikeda and Hamaguchi (1975) J. Biochem. 77, 1-16). The pH dependence of the binding of beta-GlcNAc to hen lysozyme was essentially the same as that for turkey lysozyme. The pH dependence curves of the binding constants of beta-GlcNAc to hen and turkey lysozymes were interpreted in terms of the participation of Glu 35 (pK 6.0), Asp 52 (pK 3.5), Asp 48 (pK 4.5), and Asp 66 (pK 1.5). The binding constants of alpha-GlcNAc to hen and turkey lysozymes were the same below pH 3.5 but were different above this pH. The main participant residues in the binding of alpha-GlcNAc were Glu 35, Asp 48, and Asp 66 for hen lysozyme and Glu 35 and Asp 66 for turkey lysozyme. The results obtained here were well explained by the following assumptions: (1) above about pH 4, alpha-GlcNAc binds to hen lysozyme in both alpha- and beta-modes, which correspond to the binding orientation of alpha-GlcNAc and that of beta-GlcNAc, respectively, as determined by X-ray crystallographic studies, but it binds predominantly in the beta-mode below about pH 4, (2) beta-GlcNAc binds to hen and turkey lysozymes predominantly in the beta-mode above about pH 4 and in both alpha- and beta-modes below pH 4, and (3) alpha-GlcNAc binds to turkey lysozyme predominantly in the beta-mode over the whole pH range studied.  (+info)