Modifications to chromosomal proteins help ensure that brain-specific sugars are produced only in appropriate tissues

The ß1,6-branched O-mannosyl glycan appears only in the mammalian brain. Naoyuki Taniguchi’s team at the RIKEN Advanced Science Institute in Wako recently characterized the enzyme, N-acetylglucosaminyltransferase IX (GnT-IX, also called GnT-Vb) that produces this particular glycan variant1 (Fig. 1). “We knew that some glycan-synthesizing enzymes are expressed in restricted tissues, but did not know how they are expressed,” says Yasuhiko Kizuka, a researcher in Taniguchi’s laboratory. “This led us to investigate how GnT-IX is specifically expressed in the brain.” 

Many genes are regulated by so-called ‘epigenetic mechanisms’, in which gene expression is modulated via modification of the histone protein scaffold that supports chromosomal DNA, and the researchers began by examining this possibility. When histone proteins undergo a modification known as acetylation, nearby genes are typically activated; conversely, removal of this acetylation has an inhibitory effect. 

Taniguchi and colleagues determined that the gene encoding GnT-IX is typically maintained in an inactive, non-acetylated state in 3T3-L1, a cell line derived from the fibroblasts that form connective tissue. However, when the researchers treated these cells with a drug that promotes histone acetylation, they strongly expressed GnT-IX. The brain tumor-derived Neuro2A cell line, however, naturally expresses high levels of GnT-IX. The researchers found that these cells normally maintain the chromatin near this gene in a state that stimulates activation.

In subsequent experiments, Kizuka and Taniguchi not only identified specific DNA sequences that directly regulate GnT-IX activity, but also two proteins that bind to these sites to drive expression. They found one of these factors, CTCF, in both 3T3-L1 and Neuro2A cells, but its recruitment to the GnT-IX gene was far stronger under the favorable histone modification conditions found in the latter cells. 

Intriguingly, a preliminary screen of four other glycosylation enzymes suggested that similar mechanisms govern their tissue-specificity. “Our work suggests that expression of many other glyco-genes could be regulated epigenetically,” says Kizuka.

In future studies, the researchers intend to explore how this regulatory mechanism plays into the bigger picture of glycan function. “Our group has been trying to elucidate the ‘glycan cycle’—how glycans are dynamically synthesized, play diverse roles and are degraded—using a systems biology approach,” says Kizuka. “This work tells us that epigenetic regulation is a part of this cycle.”

More information: Kizuka, Y., et al. Brain-specific expression of N-acetylglucosaminyltransferase IX (GnT-IX) is regulated by epigenetic histone modifications. The Journal of Biological Chemistry published online, 19 July 2011. doi: 10.1074/jbc/M111.251173

Provided by RIKEN (news : web)

Researchers produce cheap sugars for sustainable biofuel production

Iowa State University's Robert C. Brown keeps a small vial of brown, sweet-smelling liquid on his office table.

"It looks like something you could pour on your pancakes," he said. "In many respects, it is similar to molasses."

Brown, in fact, calls it "pyrolytic molasses."

That's because it was produced by the fast pyrolysis of biomass such as corn stalks or wood chips. Fast pyrolysis involves quickly heating the biomass without oxygen to produce liquid or gas products.

"We think this is a new way to make inexpensive sugars from biomass," said Brown, an Anson Marston Distinguished Professor in Engineering, the Gary and Donna Hoover Chair in Mechanical Engineering and the Iowa Farm Bureau Director of Iowa State's Bioeconomy Institute.

That's a big deal because those sugars can be further processed into biofuels. Brown and other Iowa State researchers believe pyrolysis of lignocelluslosic biomass has the potential to be the cheapest way to produce biofuels or biorenewable chemicals.

Brown and Iowa State researchers will present their ideas and findings during tcbiomass2011, the International Conference on Thermochemical Conversion Science in Chicago Sept. 28-30. On Thursday, Sept, 29, Brown will address the conference with a plenary talk describing how large amounts of sugars can be produced from biomass by a simple pretreatment before pyrolysis. He'll also explain how these sugars can be economically recovered from the products of pyrolysis.

A poster session following Brown's talk will highlight thermochemical technologies developed by 19 Iowa State research teams, including processes that:
increase the yield of sugar from fast pyrolysis of biomass with a pretreatment that neutralizes naturally occurring alkali that otherwise interferes with the release of sugarsprevent burning of sugar released during pyrolysis by rapidly transporting it out of the hot reaction zonerecover sugar from the heavy end of bio-oil that has been separated into various fractionsseparate sugars from the heavy fractions of bio-oil using a simple water-washing process.In addition to Brown, key contributors to the pyrolysis research at Iowa State include Brent Shanks, the Mike and Jean Steffenson Professor of Chemical and Biological Engineering and director of the National Science Foundation Engineering Research Center for Biorenewable Chemicals based at Iowa State; Christopher Williams, professor of civil, construction and environmental engineering; Zhiyou Wen, associate professor of food science and human nutrition; Laura Jarboe, assistant professor of chemical and biological engineering; Xianglan Bai, adjunct assistant professor of aerospace engineering; Marjorie Rover and Sunitha Sadula, research scientists at the Center for Sustainable Environmental Technologies; Dustin Dalluge, a graduate student in mechanical engineering; and Najeeb Kuzhiyil, a former doctoral student who is now working for GE Transportation in Erie, Penn.

Their work has been supported by the eight-year, $22.5 million ConocoPhillips Biofuels Program at Iowa State. The program was launched in April 2007.

Brown said Iowa State will – literally – take a bus load of students and researchers to the Chicago conference to present their work on thermochemical technologies, including production of sugars from biomass.

"The Department of Energy has been working for 35 years to get sugar out of biomass," Brown said. "Most of the focus has been on use of enzymes, which remains extremely expensive. What we've developed is a simpler method based on the heating of biomass."

Provided by Iowa State University (news : web)

Sugars can do it too: Protein-like oligomerization of carbohydrates

In order for enzymes and other proteins in our bodies to work correctly, it is often necessary for multiple protein units to gather together into a larger structure. Chains of sugar molecules cannot do this—at least that is what was thought until now. A team led by Thomas Heinze at the University of Jena (Germany) and Stephen E. Harding at the University of Nottingham (UK) has now proven the opposite.

In the journal Angewandte Chemie, the researchers have introduced their discovery: cellulose-like carbohydrates that can form defined aggregates from several subunits.

The individual protein subunits of functional proteins are not chemically bound to each other; they are held together by physical attractive forces and can separate again depending on the environmental conditions. It was previously assumed that molecules made of many sugar units, known as polysaccharides, never demonstrate such behavior. Defined, reversible aggregates of several such sugar chains have not previously been observed. A German–British team of researchers has now detected the protein-like aggregation of carbohydrates into defined oligomers—a novel and completely unexpected phenomenon.

The scientists studied a nitrogen-containing polysaccharide that resembles cellulose. Cellulose is the primary component of plant cell walls and is the most familiar representative of the polysaccharide family after starch. The researchers examined aminocelluloses by means of analytical ultracentrifugation. Ultracentrifuges rotate up to 500,000 times a minute. The correspondingly high centrifugal forces cause large molecules to sediment, or settle to the bottom. The sedimentation rate can be used to determine the approximate molar masses of macromolecules. In their study, the researchers found up to five different species present in their aminocellulose solutions. Their molar masses were found to be multiples of the mass of the monomer, clearly showing that they are aggregates of two to five polysaccharide units. The aggregates dissociate when the solution is diluted, indicating that the bonds are reversible.

The researchers believe that aminocelluloses not only interact with each other in this way, but also with certain other biomolecules. They could thus be interesting as boundary surface materials with biological recognition functionality, which could be used to immobilize proteins, for example to design analysis device outside a lab to identify toxins or pathogens without a few minutes. These are interesting for the on-site detection of animal diseases, food contamination as well as of biological warfare agents such as anthrax, ebola, and botulinus toxin.

More information: Thomas Heinze, Protein-Like Oligomerization of Carbohydrates, Angewandte Chemie International Edition, http://dx.doi.org/ … ie.201103026

Provided by Wiley (news : web)