IIT Guwahati's breakthrough in carbohydrate transport

GUWAHATI: Indian Institute of Technology- Guwahati researchers have shown how some specialized protein molecules found on the cell membranes of all biological cells carry carbohydrate molecules into cells from outside.

They have studied specific protein molecules called ABC transporters, present in bacterial cell membranes and have shown that these transporters are selective about the type of carbohydrates they transport into cells.

The research team is led by Dr. Shankar Prasad Kanaujia, Associate Professor, Department of Biosciences and Bioengineering, IIT Guwahati. The work has been published in The FEBS Journal and the paper has been authored by Dr. Shankar Prasad Kanaujia and his Ph.D. students – Ms. Monika Chandravanshi and Ms. Prerana Gogoi.

Any living cell needs glucose for life-sustaining energy. Glucose in turn is obtained by the breakdown of carbohydrates – table sugar (sucrose), a simple carbohydrate, and starch, a complex carbohydrate, are some sources of glucose in the cell. Such carbohydrates must be taken into the cell, and broken down inside the cell into glucose. These carbohydrates are large molecules that cannot penetrate the membranes that surround the cell by themselves and depend on some special helpers or transporting molecules to carry them across.

"One of the largest classes of transporting molecules is the ATP-Binding Cassette (ABC) transporter, which is widespread in all forms of life", says Dr. Kanaujia. These special form of proteins present in the cell membranes of almost all living cells, capture the carbohydrates from outside the cell and deliver them into the cells.

Table sugar and starch are only two of the numerous carbohydrates that are used by the cells, and they have to be preferentially taken into the cell. While ABC transporters have been known for a long time, it remains unknown if these carbohydrate-ferries have preference for specific carbohydrates over others.

The IIT Guwahati team studied the ABC Transport system of a bacterium called Thermus thermophilus that are present in hot springs. In order to survive the extreme environment, the bacterium utilizes many kinds of carbohydrates for energy. Is the ABC transport system in this bacterium inherently selective to specific carbohydrates or does it have no such preference? This is the question they have answered in their research.

"Based on the preliminary analysis of the ABC transport systems of the bacteria we chose, we hypothesized that it would have different affinities for different carbohydrates," says Dr. Kanaujia. To validate this hypothesis, the team used X-ray crystallography techniques to determine the three-dimensional crystal structure of the ABC transport system connected to various types of carbohydrates having different kinds of glycosidic bonds. "The specific ABC transporters we studied had increased affinity to the alpha-glycosidic bonds", says the lead researcher, a press release said.

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