NEWS Using neutron reflectometry, researchers at the Department of Chemistry, Umeå University, provide new atomic-level understanding of how Bax, a protein that helps remove damaged cells in the body, works. The results of the study, conducted in collaboration with the ESS research facilities in Lund and ISIS in the UK, are published in the journal Science Advances.
Dr.Luke Clifton at OffSpec, an advanced neutron reflectometer at the ISIS research facility at Harwell, UK, used to measure the interaction of the Bax protein with the membrane (see yellow arrow).
ImageSTFC (UK)"This work is relevant for understanding basic cellular processes and the biological process behind cancer" says Gerhard Gröbner, Professor at the Department of Chemistry, Umeå University. ”It also demonstrates the usefulness of neutron reflectometry. The method generates unique information at the molecular level in biophysical and biomedical research and opens up the understanding of the relationship between aging and cancer.”
This work is relevant for understanding basic cellular processes and the biological process behind cancer
Programmed cell death involves the controlled removal of harmful and superfluous cells in the body. The process is fundamental to keeping us healthy. Therefore, programmed cell death is tightly regulated by a family of key proteins called the Bcl-2 family, which includes the cell-killing protein Bax.
Gerhard Gröbner.
ImageTobias SparrmanThese proteins have opposing functions, some are cell-protective while others are cell-killing. A healthy cell has a balanced equilibrium between the different Bcl-2 proteins. However, an imbalance between these proteins during programmed cell death can interfere with the development of the embryo during the fetal stage, and can also lead to various diseases, mainly cancer.
'However, cancer cells are able to protect themselves against the effect of the cell-killing protein Bax, which is generally a problem in cancer treatment” says Gerhard Gröbner and his colleague Jörgen Ådén.
To remove harmful cells, the body activates cell-killing proteins such as Bax. Activated Bax perforates the outer membrane part of the mitochondria (the cell's powerhouse), causing the cell to die. Unfortunately, elevated levels of the cell-protecting membrane protein Bcl-2 block the action of the Bax protein. This is a major cause of growth and treatment resistance in many tumors.
”Developing a molecular understanding of how Bax attacks mitochondria may therefore open the way for the development of, for example, Bax-optimized anti-cancer drugs" says Gerhard Gröbner.
However, how the cell-killing Bax protein binds to mitochondrial membrane surfaces and performs its function is poorly understood, as detailed images and structures of the membrane were previously unavailable.
Schematic model of the Bax protein (purple) perforating the mitochondrial outer membrane (brown, lipid fatty chains; light green, lipid head groups) detected by neutron reflectometry (top). The formation of protein/lipid complexes occurs on the same timescale (a few hours) as in living cells. Generation of pores with Bax (right side; in the middle with only water (blue) are key steps to complete the programmed cell death.
ImageLuke Clifton, STFC (UK).In the current study, the researchers mainly used the neutron reflectometry (NR) technique together with an advanced instrument at the ISIS neutron facility in England, in close collaboration with the ESS in Lund, which is currently under construction.
They studied the structure of Bax in different membrane environments and with time-resolved experiments they were able to see how Bax forms pores in the membrane. This provided a molecular and mechanistic insight into this critical process during cell death.
Key collaborators have been Dr. Luke Clifton at ISIS and Dr. Hanna Wacklin-Knecht, ESS, and the Department of Physical Chemistry at Lund University. The collaboration was made possible thanks to the Swedish Research Council's specially targeted project grant. The project is a good example of how neutrons can be used in groundbreaking research and also prepares other research groups in how the technology can be used.
”In future experimental studies, we hope to find out how overproduction of the cell-protecting Bcl-2 protein and cell-killing Bax interact in membranes to understand the mechanism of how tumor cells avoid programmed cell death" says Gerhard Gröbner.
Luke Clifton, Hanna P. Wacklin-Knecht, Jörgen Ådén, Ameeq Ul Mushtaq, Tobias Sparrman, Gerhard Gröbner, Creation of distinctive Bax-lipid complexes at mitochondrial membrane surfaces drives pore information to initiate apoptosis, Science Advances, DOI 10.1126/sciadv.adg7940
