The structure offers insight into the molecular "sugar-coating" mechanism, and may help scientists better understand a variety of diseases that result when the process goes awry. The research will appear in the March 12, 2008, issue of the journal Structure.
"Proteins perform their functions by interacting at their surfaces with other molecules. So you can imagine that adding or removing sugar molecules will change the protein's surface structure, and therefore its function," said Huilin Li, a biologist at Brookhaven Lab who holds a joint appointment at Stony Brook and is co-corresponding author on the Structure paper. "Messing up this process can lead to the production of malformed proteins that are unable to do their jobs," he added.
The results can be devastating. Failure of glycosylation, as the "sugar-coating" process is known, can lead to a variety of genetic disorders characterized by neurological problems including seizures and stroke-like episodes, feeding disorders, and possibly even some forms of muscular dystrophy.
"We studied one enzyme involved in glycosylation, the one that recognizes the protein sequence and adds the sugar chains to the protein as it is being synthesized by the cell," said William J. Lennarz of Stony Brook University, a coauthor on the paper. "The challenge is that the enzyme, known as oligosaccharide transferase (OT), is large by protein standards, has eight intricately linked components, and sits embedded in a membrane within the cell's protein-manufacturing machinery."
"Membrane proteins, particularly large ones, are very difficult to study structurally," added Li.
So the scientists turned to a technique called cryo-electron microscopy (cryo-EM), which shows great promise in deciphering large membrane protein structures.
"We imaged the purified OT complex by cryo-EM and obtained a first snapshot of the complex by computer reconstruction of the micrographs," said Li, a cryo-EM expert.
In cryo-EM, he explained, samples are frozen in vitreous ice and maintained at cryogenic temperatures (-274° Fahrenheit) using liquid nitrogen while the samples are photographed in the high vacuum of an electron microscope. The sophisticated cryo-EM machine resides in Brookhaven Lab's biology department. Li and his collaborators also measured the mass of the OT complex at Brookhaven's Scanning Transmission Electron Microscope (STEM) facility.
The structure deciphered by the group helps to explain many biochemical phenomena observed about the enzyme complex over the past two decades. It also offers hints as to how the enzyme performs its various jobs, from recognizing the sugar molecules to be added to the protein, scanning the protein as it is formed to identify the sites where sugars should be attached, and transferring the sugar molecules to the protein at the right positions.
"OT physically associates with the protein translocation channel which moves a protein across a membrane and the cell's protein synthesis machinery, forming an efficient three-machine assembly line for protein translation, translocation, and glycosylation," Li said.
The researchers say further research is needed to illuminate the molecular mechanisms of disorders of glycosylation involving oligosaccharide transferase. For example, they would like to do structural studies of the enzyme at higher resolution in complex with substrates or in association with the cell's protein translocation and protein synthesis machinery. A new facility Brookhaven Lab hopes to begin construction on next year, known as the National Synchrotron Light Source II, would greatly increase the precision of this work.
How brains surrender to sleep
23.06.2017 | IMP - Forschungsinstitut für Molekulare Pathologie GmbH
A new technique isolates neuronal activity during memory consolidation
22.06.2017 | Spanish National Research Council (CSIC)
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
23.06.2017 | Physics and Astronomy
23.06.2017 | Physics and Astronomy
23.06.2017 | Information Technology