Mitochondria, considered powerhouses that reside in human cells, produce the energy necessary for cell survival. Yet, as a byproduct of this process, mitochondria also generate reactive oxygen species (ROS).
These ROS are very destructive at high concentrations, instigating oxidative damage and even killing cells. Excessive amounts of ROS have been linked to various health problems, such as cancers, heart disease, and neurological disorders.
To address this, researchers have revealed an antioxidant enzyme targeted for therapeutic use. Manganese superoxide-dismulase or MnSOD allows electron and proton transfers to decrease ROS levels in mitochondria, thus avoiding oxidative damage and preserving its health. A considerable number of enzymes, around a quarter of them, depending on electron and proton transfers to enable cellular activities fundamental to a person's health. However, their mechanisms are not clear due to the challenges in observing the movement of photons.
Scientists from the University of Nebraska Medical Center (UNMC) and the Department of Energy's Oak Ridge National Laboratory have now studied MnSOD's atomic structure, and this includes its proton arrangements with neutron scattering, Results of their study published in Nature Communications show how protons are utilized as tools to assist MnSOD transfer electrons to decrease ROS levels. The findings could guide experts in developing MnSOD-based treatments and creating therapeutic drugs that imitate its antioxidant behavior. It also provides an opportunity for further research on enzymes that use electron and proton transfer.
Unexpected MnSOD Features Revolutionize Enzyme Perception
Researchers used neutrons to study unexpected MnSOD features, revolutionizing how people look at how these enzymes or other similar enzymes operate.
MnSOD works by zeroing in on superoxide, a reactive molecule leaking from the mitochondrial energy production process and a chemical precursor for other destructive ROS. The active site of the enzyme transforms superoxide into lesser toxic products using manganese ion to bring electrons to and from the reactive molecule. This manganese ion can steal an electron from a superoxide molecule, changing it to oxygen. The stolen electron can be passed on to another superoxide to produce hydrogen peroxide.
To make this biochemical reaction work, proton movements are necessary between the amino acid of the enzyme and other active molecules. Protons serve as a tool that would make electrons move. The enzyme's catalytic mechanism, or its sequence of electron and proton transfers, had not been defined at the atomic level due to challenges in monitoring the shuttling of protons between molecules. A basic understanding of this catalytic process could boost therapeutic strategies that could control the antioxidant abilities of the enzyme.
Proton transfers are not easily observed because they happen in the form of atomic hydrogen, which x-rays and other methods for atom observation find difficult in detecting. On the other hand, neutrons are proven to be sensitive to lighter elements, such as hydrogen, and can identify proton movements. Neutrons are also ideal for research since they do not interact with electrons, unlike other atom-visualizing approaches. It can also be used to look into the inner workings of electron-transfer enzymes without disrupting their electronic state.
Building a Model of Catalytic Mechanism
Using macromolecular neutron diffractometer MaNDI at the ORNL's Spallation Neutron Science (SNS), researchers mapped out MnSOD's electronic structure and monitor how the protons in the enzyme change as it gains or loses an electron. By studying neutron data, scientists discovered the protons' pathways as they move around the active site. Using these data, researchers constructed a model of the proposed catalytic mechanism, showing how electron and proton transfers allowed MnSOD to control superoxide levels.
The study suggests that catalysis would entail two internal proton transfers between the enzyme's amino acids and two external proton transfers that come from solvent molecules. While the study findings confirm previous predictions of the enzyme's biochemical nature, several aspects turn out to be unexpected and dispute previously held beliefs.
To illustrate, researchers observed cyclic proton transfers occurring between a manganese-bound solvent molecule and a glutamine amino acid. This forms the central part of the catalytic process, allowing the enzyme to cycle between its two electronic states. The team also discovered unusual proton movements within the active site since a number of amino acids lacked a proton that they normally should have. Their study also showed the remarkable effects of metal on the chemistry of the active site that were previously unreported.
Researchers plan to study the structure of the enzyme that is attached to a superoxide substrate. They also target to study mutated components of MnSOD to get more information on how the amino acids impact catalysis. They also envision expanding neutron analysis to other enzymes that depend on electron and proton transfers to complete cellular tasks.
RELATED ARTICLE : Scientists Have Discovered An Effective Antioxidant To Slow Down Aging Process of The Human Skin
Check out more news and information on Antioxidants and Enzymes on Science Times.
