In eukaryotic cells, which are found in complex organisms including humans, little membrane-bound organelles carry out various functions. It's been suggested that these organelles, which all have distinctive functional and physical characteristics, may have a form that reflects their function. For example, proteins travel through different parts of the wavy, multi-layered Golgi apparatus where they are modified in various ways along the way. Another example could be mitochondria, essential cellular powerhouses that use their membranes to generate energy for the cell. Researchers have now created a tool that can test how form follows function in cells. The work has been published in Cell Reports.
In this study, the researchers used the technique to target the outer membrane of organelles and dismantle it. This work may eventually help scientists treat illness; the investigators suggested that might also be useful for breaking up deleterious proteins that can accumulate in cells and cause disease, like in neurodegenerative conditions, although more work would be needed to determine if that can work.
This new tool could also help show how the function of organelles can change when their shape is altered, for better or worse, said study co-author Takanari Inoue, PhD, a professor at Johns Hopkins University. The interior parts of mitochondria can become disorganized as these organelles enlarge in Alzheimer's, noted Inoue. In the accelerated aging disease known as progeria, patients have cells with a misshapen nucleus.
In this work, the investigators used the powers of Listeria, an infectious microbe that teds to cause foodborne illness in people. These microbes can absorb nutrients from cells they infect, then move on to infect other cells. The researchers measured the physical forces that are created as Listeria takes control of a protein called actin. Listeria that was bound to actin was used to assemble various molecules that link to an organelle's surface, then exert enough force to break it open. The new tool has been called ActuAtor.
ActuAtor was tested on human epithelial cells to show that the tool can fragment mitochondria completely within ten minutes of Listeria entering cells.
The technique also did not seem to damage the organelles, since there was little difference in how much power was generated before and after ActuAtor was applied. The cell did react to these altered mitochondria, however, and moved to eliminate some of them.
"In this case, our team concluded that function may not follow form in mitochondria," says Inoue.
ActuAtor was also used to open nuclei and Golgi bodies. The investigators modified ActuAtor to disrupt proteins that had formed granules due to environmental stress, like low oxygen levels or temperature changes. Further testing on this application and how it might be used to treat diseases is now planned, said the researchers.