Biological complexity: how cells maintain phosphate levels (Introduction)

by David Turell , Thursday, April 14, 2016, 21:41 (3145 days ago) @ David Turell

As usual it is a complex mechanism which is important because phosphate is a major ingredient in all the ATP mechanism, the energy source of the cell:-http://phys.org/news/2016-04-cellular-sensor-phosphate.html-"Researchers from the University of Geneva (UNIGE) and the University of Lausanne (UNIL), Switzerland, report that a region of specific proteins, the so-called SPX domain, signals the phosphate status to fungal, plant and human cells. This domain provides a binding surface for small molecules that regulate the uptake of the nutrient into the cell.-***-"Michael Hothorn, Professor at the Department of Botany and Plant Biology of the Faculty of Science of UNIGE, and his research group revealed the crystal structure of a novel protein domain called SPX, which is involved in many phosphate signaling pathways. They discovered that SPX provides a binding surface for small compounds called inositol pyrophosphate signaling molecules (InsP), which can interact with other proteins only when they are bound to the SPX domain. As SPX domains can be attached to different proteins, such as enzymes, transporters or signaling proteins, the biologists hypothesized that InsP regulate various cell processes involved in phosphate homeostasis, from yeast to human cells.-***-"'We found out that the concentration of InsP changes in response to phosphate availability. InsP levels are high in cells that have sufficient phosphate, and drop when phosphate becomes scarce," explains Ruta Gerasimaite from UNIL, one of the first co-authors of the study. "In phosphate-starved plants, specific transcription factors turn on the expression of phosphate transporter genes. Once the plant is satiated, SPX domains filled with InsP will bind and inactivate these transcription factors, and no more phosphate will be absorbed from the soil into the cell," says Rebekka Wild from UNIGE, another of the first co-authors.-***-"The role of InsP was initially elucidated in yeast cells: "We came across InsP while studying the mechanism of phosphate polymerization - its assembly into long chains - for the storage of this compound, and our data show that the SPX domain is a receptor for InsP," states Andreas Mayer, Professor at the Department of Biochemistry of UNIL. Once the SPX domain is filled, it activates the enzyme involved in phosphate storage.-Comment: this is a typical closed-loop feedback system to control levels. One wonders how such a complex system develops all of its parts at once. Consider the cells must have a steady level of phosphate as a fuel. It suggests the entire system appeared all at once.