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‘Pedal bin machine’ of gut bacteria revealed

A nutrient molecule (green) overcomes the cell membrane (grey) of a bacterium with the help of a channel protein (SusC, yellow). The graphic shows how this process is supported by a substratebinding protein (SusD, in pink) as well as lipoproteins (SusEF, in blue). Graphics: Karunakar R. Pothula / Jacobs University

January 11, 2017

Researchers from Newcastle University and Jacobs University have shed new light on the functioning of gut bacteria, revealing how nutrients are transported into bacterial cells. Their findings increase existing knowledge about the microbiota which has been linked to the emergence of autoimmune diseases, cancer, and obesity.
The researchers, led by Professor Bert van den Berg from Newcastle University and including Professor Ulrich Kleinekathöfer and Professor Mathias Winterhalter from Jacobs University in Bremen, report their findings today (January 11, 2017) in Nature.
The human large bowel ("gut") is colonized by an extremely dense population of bacteria, collectively termed the microbiota or "gut flora".
Recent research indicates that the microbiota is important for human health and nutrition and has been linked with autoimmune diseases, cancer, and obesity. The function and composition of the microbiota are dependent on the ability of individual microorganisms to acquire nutrients such as starch and other dietary polysaccharides in the highly competitive environment of the human large bowel.
This process of nutrient acquisition is carried out by protein machines embedded in the bacterial cell envelope. In many microbiota members, this machine is a two-component complex consisting of a substrate-binding protein (termed SusD) and a channel-forming transport protein (termed SusC).
The scientists at Newcastle University today report that they determined the first three-dimensional atomic structures of SusCD complexes by X-ray crystallography. Based on this structural data, the Kleinekathöfer group from Jacobs University performed molecular simulations. Using biophysical techniques, the transport properties of the channel-forming protein SusC were analyzed by the Winterhalter group. The research of the scientists from Bremen shows: The SusCD complexes function like a pedal bin, with SusD forming the lid on the SusC bin. In the absence of substrate, the lid can open. After substrate capture, the lid closes and the substrate moves into the bin for transport into the cell.
“We are very happy that our knowledge as biophysicists helped to answer a question of possible medical importance while we worked in this international and interdisciplinary research group”, Kleinekathöfer and Winterhalter state.
The study provides fundamental insights into the functioning of the microbiota and understanding the human-gut flora symbiosis. Results such as these are a necessary complement to most current microbiota research, which is largely focused on answering systems biology questions such as which bacteria are in the human large bowel and under which conditions.
Additional information at:
Reference: Structural basis for nutrient acquisition by dominant members of the human gut microbiota
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