Solving the puzzle of the cell membrane

April 19th 2018

A study by researchers at Biopark sheds light on mysterious structures identified in 2003 in the cell's membrane. A process that had never been elucidated… until now!

In 2003, a team of German researchers observed a strange phenomenon at the surface of yeast cells: some of the membrane's transporters gathered into local invaginations, with no apparent purpose. These transporters are specific proteins catalysing nutrient uptake into the cell. This clustering of transporters was a rather surprising discovery, as cell membrane proteins are usually spread out evenly across the surface. Researchers at the time were unable to explain their observation, but the puzzle has now been solved!

A matter of conformation

Professor Bruno André’s Molecular Cell Physiology laboratory (Department of molecular biology, IBMM) can now provide some insight into the process. The study was conducted in collaboration with UCL and the CMMI imaging centre, and has been published in science journal PNAS. Experiments on yeast have first shown that the transporters accumulate in these membrane invaginations only when adopting a specific 3D structure.

Protecting from autophagy

The researchers explain that these specific membrane invaginations protect membrane transporters from being eliminated when a nutritional deficiency occurs. When there is no food, the cell begins a process known as autophagy: it gradually digests its own components, including the proteins in its membrane. When gathered together into these clusters, the transporters are protected from degradation: they remain present in large numbers in the membrane, and can be operational as soon as nutrients become available once again. Similar ‘microdomains’ have been observed in human cells, but little is currently known about them; this study is a first step towards understanding their function in humans.

Another mystery…

Researchers at Professor André's laboratory have authored another study on how cells react to nutrient availability. Published in eLife, it deals with a molecular complex called TORC1. The researchers have elucidated how is this complex activated after amino acids — the fundamental building blocks of proteins — are transported across the cell membrane. A flow of protons (H ), regulated by enzymes found in the membrane, occurs at the same time. The main enzyme responsible for the flow of protons plays an essential part in activating TORC1, and the researchers are now attempting to learn more about this relationship. Their current hypothesis is that the enzyme promoting proton flow triggers a signalling cascade that eventually reaches TORC1 and plays an important in control of cell growth.