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Biomedical subjects

R I Hollingsworth

Publications and source records attributed to R I Hollingsworth.

At least 19 recordsLinked to original sources
PubMed2002

Physiological function of alcohol dehydrogenases and long-chain (C(30)) fatty acids in alcohol tolerance of Thermoanaerobacter ethanolicus.

A mutant strain (39E H8) of Thermoanaerobacter ethanolicus that displayed high (8% [vol/vol]) ethanol tolerance for growth was developed and characterized in comparison to the wild-type strain (39E), which lacks alcohol tolerance (<1.5% [vol/vol]). The mutant strain, unlike the wild type, lacked primary alcohol dehydrogenase and was able to increase the percentage of transmembrane fatty acids (i.e., long-chain C(30) fatty acids) in response to increasing levels of ethanol. The data support the hypothesis that primary alcohol dehydrogenase functions primarily in ethanol consumption, whereas secondary alcohol dehydrogenase functions in ethanol production. These results suggest that improved thermophilic ethanol fermentations at high alcohol levels can be developed by altering both cell membrane composition (e.g., increasing transmembrane fatty acids) and the metabolic machinery (e.g., altering primary alcohol dehydrogenase and lactate dehydrogenase activities).

Alcohol Dehydrogenase↗
PubMed2000

A general approach to the synthesis of dideoxy and trideoxyiminoalditols from beta-D-glycosides.

Imino sugars (also called azasugars), a class of compounds of which the 1,5-dideoxy and 1,5,6-trideoxyiminoalditols are members, are important glycosidase inhibitors with very high potential as drugs. Their potential therapeutic applications range from the treatment of diabetes to cancer and AIDS. We present here a general method for the preparation of such compounds with the D-gluco and D-galacto configurations starting from beta-D-glycosides. The procedure is especially appealing because of its high stereoselectivity and straightforwardness. The key steps are the selective oxidation of the glycosides to hexulosonic acids and reduction of the oxime derivatives to lactams, which are further reduced to the target compounds. The C-6 position can be deoxygenated during the reduction if it bears an acetoxy group. Trideoxy imino sugars are then produced. Deacetylation prior to oxime reduction gives dideoxy compounds.

Aza Compounds↗
PubMed1999

Ozonolytic depolymerization of polysaccharides in aqueous solution.

The selective oxidation of beta-D-glycosidic linkages of polysaccharides by ozone has great utility as a general method for depolymerization of polysaccharides. Here we describe a 'one-step' method whereby polysaccharides dissolved in water or basic solutions are depolymerized by ozonolysis. The oxidation of glycosidic linkages of unprotected carbohydrates by ozone is complicated by several side reactions. We describe here optimized conditions for carrying out ozonolysis degradation. We also characterize the major pathways for unwanted degradation by various side reactions. In the preferred oxidation pathway, the aldosidic linkage is oxidized to an aldonic ester function that hydrolyzes under the basic conditions employed to give a free aldonate, with cleavage of the polysaccharide chain. Nonselective degradation pathways include oxidative degradation by radical species that oxidize glycosyl residues to formic, acetic, and oxalic acids. The nonselective degradation caused by acids is minimized by basic buffers. The products of polysaccharide depolymerization form a size distribution around a nominal molecular weight, and the average molecular weight of the products can be controlled by the rate or amount of ozone passed through the reaction mixture. The ozonolysis method described herein provides a convenient, inexpensive, and controllable means for generating small polysaccharides or large oligosaccharide fragments.

Bacterial Capsules↗
PubMed1998

Ozonolysis for selectively depolymerizing polysaccharides containing beta-D-aldosidic linkages.

The depolymerization of polysaccharides, particularly those containing acid-sensitive components, into intact constituent repeating units can be very difficult. We describe a method using ozonolysis for depolymerizing polysaccharides containing beta-D-aldosidic linkages into short-chain polysaccharides and oligosaccharides. This method is carried out on polysaccharides that have been fully acetylated whereby beta-D-aldosidic linkages are selectively oxidized by ozone to form esters, from which the polysaccharides are subsequently cleaved with a nucleophile. Ozone oxidation of aldosidic linkages proceeds under strong stereoelectronic control, and reaction rates depend on the conformations of glycosidic linkages. Thus, beta-D-aldosidic linkages with different conformations can have very different reaction rates even in the absence of substantial chemical differences. These rate differences allowed for very high selectivity in cleaving beta-D-linkages of polysaccharides. Several polysaccharides from group B Streptococcus and other bacterial species were selectively depolymerized with this method. The repeating units of the group B Streptococcus polysaccharides all contain an acid-sensitive sialic acid residue in a terminal position on a side chain and several beta-D-residues including galactose, glucose, and N-acetylglucosamine; however, with each polysaccharide, one type of linkage was more reactive than others. Selective cleavage of the most sensitive linkage occurs randomly throughout the polymer chain, yielding fragments of controllable and narrowly distributed sizes and the same repeating-unit structure. The average size of the molecules decreases exponentially, and desired sizes can be obtained by stopping the reaction at appropriate time points. With this method the labile sialic acid residue was not affected.

Carbohydrate Sequence↗
PubMed1998

Structural analysis of leech galactocerebrosides using 1D and 2D NMR spectroscopy, gas chromatography-mass spectrometry, and FAB mass spectrometry.

Cerebrosides were isolated from the leech species, Hirudo medicinalis, and purified to homogeneity by silicic acid chromatography, followed by preparative thin-layer chromatography. Their structure was determined by spectroscopic and chemical methods. 1D and 2D 1H NMR spectroscopy, DQF-COSY and HMQC indicated that the head group consists of a single galactose residue in the beta configuration. The galacto configuration was determined by the characteristic chemical shift, the spin-spin splitting and the multiplicity of the characteristic resonance of its equatorial H-4 proton, as well as by the splittings of the other ring protons. GC, GC-MS and fast-atom-bombardment mass spectrometry studies indicated that C24:0 and C22:0 are the major saturated fatty acid species. Unsaturated fatty acids present were C25:2, C27:2, C27:3, C28:3, C29:3, C30:3, C33:3. GC-MS indicated the presence of hydroxylated C27:2 and one other unidentified hydroxylated fatty acid. The cerebroside contained an unusual polyunsaturated sphingosine analogue, namely 2-amino-1,3-dihydroxydocsatriene.

Animals↗
PubMed1998

Cholesterol and its derivatives, are the principal steroids isolated from the leech species Hirudo medicinalis.

Steroids were isolated from the blood-sucking leech species Hirudo medicinalis and their structure was studied with one- and two-dimensional NMR spectroscopy (DQF-COSY and HMQC), GC-MS and ESI-MS spectrometry. Fractionating leech lipid using silicic acid chromatography led to the isolation of cholesterol in an early chloroform-eluted peak. Only minor traces of cholest-4-en-3-one, 4 beta-methylcholesterol, and sitosterol were present. The subsequent acetone-eluted fraction contained steroidtriols that were further purified by preparative TLC; these included cholest-7-ene-3,5,6 triol, cholest-4,7-diene-3,6,15 triol and to a lesser amount, cholestane-3,5,6 triol. A developmental study on cholesterol content in the leech showed that it is also the principal steroid in embryonic and freshly hatched leeches prior to feeding. The abundance of cholesterol, comprising approximately 5% of the total leech lipid, suggests that H. medicinalis, a blood sucking leech, has adapted itself fully to its mammalian host in terms of its steroid content. It remains to be seen whether lipids are directly transferred from the host to the parasite or whether leeches have evolved mechanisms to synthesize their own steroids.

Animals↗
PubMed1998

Regulation of lipid synthesis in Bradyrhizobium japonicum: low oxygen concentrations trigger phosphatidylinositol biosynthesis.

Lowering oxygen tension in free-living Bradyrhizobium japonicum resulted in a dramatic switch of membrane chemistry in which phosphatidylcholine, the predominant lipid in aerated cultures, was no longer synthesized and phosphatidylethanolamine became the major lipid. Besides this change, phosphatidylinositol, a typical plant lipid rarely found in bacteria, was also synthesized.

Lipids↗
PubMed1997

Oligosaccharide beta-glucans with unusual linkages from Sarcina ventriculi.

The structure of a family of unusual glucans from Sarcina ventriculi has been characterized by NMR spectroscopy, methylation analysis, and mass spectrometry. One is a trisaccharide containing a beta-(1-->3) and a beta-(1-->4)-linkage. The other is a hexasaccharide that is simply a 1,4-linkage dimer of the trisaccharide unit. This is the first report of beta-glucan biosynthesis in a Gram-positive organism. Their occurrence in these organisms supports an even more general link between their synthesis and the adaptability of bacteria.

Carbohydrate Conformation↗
PubMed1997

Digalactosyl diacylglycerols, plant glycolipids rarely found in bacteria, are major membrane components of bacteroid forms of Bradyrhizobium japonicum.

The membrane lipids of free living and bacteroid forms of Bradyrhizobium japonicum, obtained from nodules occupied by both typed and untyped bacteria, were isolated and characterized by a combination of NMR spectroscopy, mass spectrometry, and other chemical and physical methods. These studies indicated that both the free living and bacteroid forms of this organism contain glycolipids almost exclusively of the type found in plant cells. In the bacteroid forms, there was a dramatic shift towards the synthesis of digalactosyl diacylglycerol as the major lipid. This glycolipid has rarely been found outside of the plant kingdom and photosynthetic bacteria, and its occurrence in the bacteroid form of a plant symbiont is therefore remarkable. The presence of plant cell and organelle contaminants in the bacteroid preparations was ruled out by scanning electron microscopy, Southern blot analyses for plant DNA using specific gene probes, and chemical analyses for plant marker steroids, steroid glycosides, and cerebrosides. Digalactosyl diacylglycerol is not found in the plasma membrane of plant cells (of which the peribacteroid membrane is an extension) but is thought to be restricted to plastids. This result follows our earlier finding that the other predominant plant glycolipid, sulfoquinivosyl diacylglycerol, is a membrane component of fast growing Rhizobia and is found even when cells are cultivated in free culture where there is no question of plant contamination. The near absence of these lipids in the membranes of bacteria outside of this special group of organisms and photosynthetic bacteria suggests that the trait could have been passed on through gene transfer from plants to the bacteria at some point during the development of their symbiotic relationship. In the case of digalactosyl diacylglycerol, there is also the possibility that some common biosynthetic intermediates are used by both the plant and the bacteria. This is a striking parallel with some host-pathogen interactions.

Carbohydrate Conformation↗
PubMed1997

Composition and role of extracellular polymers in methanogenic granules.

Methanobacterium formicicum and Methanosarcina mazeii are two prevalent species isolated from an anaerobic granular consortium grown on a fatty acid mixture. The extracellular polysaccharides (EPS) were extracted from Methanobacterium formicicum and Methanosarcina mazeii and from the methanogenic granules to examine their role in granular development. The EPS made up approximately 20 to 14% of the extracellular polymer extracted from the granules, Methanobacterium formicicum, and Methanosarcina mazeii. The EPS produced by Methanobacterium formicicum was composed mainly of rhamnose, mannose, galactose, glucose, and amino sugars, while that produced by Methanosarcina mazeii contained ribose, galactose, glucose, and glucosamine. The same sugars were also present in the EPS produced by the granules. These results indicate that the two methanogens, especially Methanobacterium formicicum, contributed significantly to the production of the extracellular polymer of the anaerobic granules. Growth temperature, substrates (formate and H(inf2)-CO(inf2)), and the key nutrients (nitrogen and phosphate concentrations) affected polymer production by Methanobacterium formicicum.

Journal Article↗
PubMed1997

Structural requirements of Rhizobium chitolipooligosaccharides for uptake and bioactivity in legume roots as revealed by synthetic analogs and fluorescent probes.

Rhizobium chitolipooligosaccharides (CLOSs) are heterogeneous fatty acylated N-acetyl glucosamine oligomers with variations in both the polar (hydrophilic) oligosaccharide head group and the non-polar (hydrophobic) fatty acyl chain. They trigger root hair deformation and cortical cell divisions in legume roots during development of the nitrogen-fixing root-nodule symbiosis. It has been proposed that only certain unique molecular species of CLOSs made by a particular rhizobia can elicit these responses on the corresponding legume host, suggesting that receptor-mediated perception of CLOSs serves as a basis of symbiotic specificity. We evaluated the relative symbiotic importance of the hydrophilic and hydrophobic structural domains of CLOSs by comparing the biological activities of CLOSs from wild type R. leguminosarum bv. trifolii ANU843 with that of various synthetic analogs. These tests were performed in axenic bioassays on the compatible symbiotic host, white clover (Trifolium repens) and the incompatible non-host legume, alfalfa (Medicago sativa). Fluorochrome-tagged derivatives of the native CLOSs and the analogs were also prepared in order to evaluate the uptake and localization patterns of these molecules within host root cells. The results indicate a direct link between uptake and biological activities of Rhizobium CLOSs on legume roots. The smallest CLOS analog taken up and biologically active on white clover and alfalfa was a N-fatty acylglucosamine, without an essential requirement of oligomerization, fatty N-acyl unsaturation, or acetate/sulfate functionalization. This suggests that N-fattyacylglucosamine is the common minimum structure required and sufficient for uptake and biological activity of CLOS glycolipids in these legumes, and that the various specific modifications of its polar head group and hydrophobic tail modulate its inherent ability to further express these activities, thus influencing which legumes are capable of responding to CLOSs rather than dictating their biological activities per se.

4-Chloro-7-nitrobenzofurazan↗
PubMed1996

An NMR spectroscopy and molecular mechanics study of the molecular basis for the supramolecular structure of lipopolysaccharides.

Lipopolysaccharides from Gram-negative bacteria interact with the mammalian immune system to trigger a cascade of physiological events leading to a shock syndrome which results in the death in over 70% of cases of severe shock. It is known that the supramolecular structures of lipopolysaccharide aggregates are critical contributors to their biological activities. Despite this, the molecular basis for the formation if the regular hexagonal plates and arrays observed in lipopolysaccharide films and suspensions is unknown. Since these structures are two dimensional, it is unlikely that X-ray crystallographic methods will shed much light on their detailed structure. Knowing this structure is important since it is becoming increasingly likely that the insertion of the lipopolysaccharide hydrocarbon chains in the target host cell membrane may be involved in triggering host responses. This work describes the three-dimensional structure of the lipopolysaccharide lipid A moiety. The structure was obtained by a combination of molecular mechanics calculations and nuclear magnetic resonance spectroscopy. This involved calculation of the dihedral angle between the two glucosamine residues of the lipid A molecule from coupling constants and measuring critical interresidue NOE values. The study also takes into account information from X-ray powder diffraction and electron microscopy studies.

Carbohydrate Conformation↗
PubMed1996

The chemical degradation of starch: old reactions and new frontiers.

The chemistry of starch degradation is reviewed from the standpoint of the general utility of the reactions and the proposed mechanisms. The limitations and potential of the various chemical transformations are discussed. The reactions discussed include hydrolysis, oxidations, base-catalyzed degradations, halogenations and radiolysis. The potential scope for starch-derived materials in industry is examined. The potential use in the manufacture of fine chemicals is explored.

Industry↗
PubMed1996

Modulation of development, growth dynamics, wall crystallinity, and infection sites in white clover root hairs by membrane chitolipooligosaccharides from Rhizobium leguminosarum biovar trifolii.

We used bright-field, time-lapse video, cross-polarized, phase-contrast, and fluorescence microscopies to examine the influence of isolated chitolipooligosaccharides (CLOSs) from wild-type Rhizobium leguminosarum bv. trifolii on development of white clover root hairs, and the role of these bioactive glycolipids in primary host infection. CLOS action caused a threefold increase in the differentiation of root epidermal cells into root hairs. At maturity, root hairs were significantly longer because of an extended period of active elongation without a change in the elongation rate itself. Time-series image analysis showed that the morphological basis of CLOS-induced root hair deformation is a redirection of tip growth displaced from the medial axis as previously predicted. Further studies showed several newly described infection-related root hair responses to CLOSs, including the localized disruption of the normal crystallinity in cell wall architecture and the induction of new infection sites. The application of CLOS also enabled a NodC- mutant of R. leguminosarum bv. trifolii to progress further in the infection process by inducing bright refractile spot modifications of the deformed root hair walls. However, CLOSs did not rescue the ability of the NodC- mutant to induce marked curlings or infection threads within root hairs. These results indicate that CLOS Nod factors elicit several host responses that modulate the growth dynamics and symbiont infectibility of white clover root hairs but that CLOSs alone are not sufficient to permit successful entry of the bacteria into root hairs during primary host infection in the Rhizobium-clover symbiosis.

Cell Wall↗
PubMed1996

The "missing" typical Rhizobium leguminosarum O antigen is attached to a fatty acylated glycerol in R. leguminosarum bv. trifolii 4S, a strain that also lacks the usual tetrasaccharide "core" component.

Rhizobium leguminosarum bv. trifolii 4S has a lipopolysaccharide O antigen that lacks galactose and many of the typical glycosyl components found in related strains. Here, we show that it also lacks the typical core tetrasaccharide but synthesizes an alternative glycolipid that contains galactose and the typical O-antigen glycosyl components, suggesting that in this strain, the O antigen is transferred to an alternative lipid acceptor.

Gas Chromatography-Mass Spectrometry↗
PubMed1995

Membrane lipid alkyl chain motional dynamics is conserved in Sarcina ventriculi despite pH-induced adaptative structural modifications including alkyl chain tail to tail coupling.

Sarcina ventriculi, an anaerobic Gram-positive bacterium, adapts to increasing temperature, the presence of organic solvents, or the lowering of the pH of its growth medium by joining the tails of membrane lipids from opposite sides of the bilayer, forming transmembrane, bifunctional fatty acid species. Since this is done to offset the increase in membrane mobility caused by these perturbations, it is of interest to determine whether the motional (dynamic) properties of membrane lipid alkyl chains are conserved. In this study, conservation of the motional time scales of the alkyl chains of total membrane lipids from Sarcina ventriculi cells grown at different pH values was demonstrated using proton nuclear magnetic resonance (NMR) spectroscopy. The NMR longitudinal relaxation times (T1) of the protons in the bulk methylene groups were measured for lipids from cells grown at pH 3.0 and 7.0. These measurements indicated that the temperature profile of the T1 relaxation behavior for the methylene protons from these two different preparations was the same. Analysis of the data from T1 measurements indicated that the thermal barrier for relaxation is the same in both lipid systems. This is only true if the pH of the sample on which the measurement is being made is adjusted to the same value as that at which the corresponding cells were cultured. It is clear from this latter observation that the state of protonation of the lipid head groups is a contributor to the overall motional freedom of the membrane lipid components. The correlation times (tau c) of characteristic lipid alkyl chain motion were estimated to be approximately 10(-10) s.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1995

Mutation or increased copy number of nodE has no effect on the spectrum of chitolipooligosaccharide nod factors made by Rhizobium leguminosarum bv. trifolii.

The bacterial gene nodE is the key determinant of host specificity in the Rhizobium leguminosarum-legume symbiosis and has been proposed to determined unique polyunsaturated fatty acyl moieties in chitolipooligosaccharides (CLOS) made by the bacterial symbiont. We evaluated nodE function by examining CLOS structures made by wild-type R. leguminosarum bv. trifolii ANU843, an isogenic nodE::Tn5 mutant, and a recombinant strain containing multiple copies of the pSym nod region of ANU843. 1H-NMR, electrospray ionization mass spectrometry, fast atom bombardment mass spectrometry, flame ionization detection-gas chromatography, gas chromatography/mass spectrometry, and high performance liquid chromatography/UV photodiode array analyses revealed that these bacterial strains made the same spectrum of CLOS species. We also found that ions in the mass spectra which were originally assigned to nodE-dependent CLOS species containing unique polyunsaturated fatty acids (Spaink, H. P., Bloemberg, G. V., van Brussel, A. A. N., Lugtenberg, B. J. J., van der Drift, K. M. G. M., Haverkamp, J., and Thomas-Oates, J. E. (1995) Mol. Plant-Microbe Interact. 8, 155-164) were actually due to sodium adducts of the major nodE-independent CLOS species. No evidence for nodE-dependent CLOSs was found for these strains. These results indicate a need to revise the current model to explain how nodE determines host range in the R. leguminosarum-legume symbiosis.

Acyltransferases↗