Difference between revisions of "Part:BBa J03210"

Maltose, a basic metabolite, is an important energy source for E. coli. It is actively sensed by cells via their natural chemotactic machinery, specifically the Tar Chemoreceptor. Extensive literature provided a very clear picture of the Maltose regulon, a self-contained, tightly regulated set of genes that control maltose uptake, taxis and metabolism.

Above – malE-encoded MPB's role in the maltose transport and taxis system.

The regulon is made up of three separate operons, all of which contain positive feedback loops that see maltose itself up-regulate the expression of the associated genes for taxis, transport and metabolism. This is done via the maltose-activated malT promoter (malTp), which regulates the expression of malT, a protein that in-turn directly regulates the three separate operons in question.

The most significant discovery concerns the key-role of the malE gene, which encodes the maltose-binding protein (MBP). Located in the periplasm, this protein is essential for both maltose transport and chemotaxis. It binds directly with maltose (and its higher homologs, the maltosedextrins), undergoing a conformational change to its structure. As result it is subsequently able to (i) interact with the membrane complex malFGK, transporting the ligand into the cytoplasm, and (ii) stimulate the cell’s sensory circuitry by binding to the Tar chemoreceptor. In essence, without MBP, a cell is neither able to detect maltose nor use it as an energy source. [The expression of the maltose regulon cannot be induced in the presence of glucose]