Chemists may now understand why some bacteria can break apart toxic substances without poisoning themselves. The answer centres on the surprising dual function of an enzyme that transforms harmful molecules into benign ones. For the first time, German researchers have discovered the precise actions of the enzyme nicknamed PaaABCE. It is known as a key player in the bacteria’s ability to dismantle and change molecules in a number of cell circumstances. The authors report their results in the journal Nature. PaaABCE, they found, is unique because it has two distinct functions. On the one hand, it can insert oxygen into a toxic substance, setting it up for degradation. On the other hand, it can remove that same oxygen. The authors speculate that this dual function allows the bacteria to keep toxic materials in the cell at low levels, thus protecting the organism from harm during the detoxification process. The report is significant because it increases understanding of the molecular mechanisms that bacteria use to detoxify their cell environments. The new insight could provide chemists with important instructions that would tell them how to dismantle old chemical pollutants and assemble new commercially viable ones that would possess decreased lifetimes in the environment. Chemists produce molecules that serve important roles in countless commercial products. Colouring agents, plasticisers, odorants and preservatives are examples. But what happens to these compounds once they are finished performing their intended function? Many are released into the environment and linger there. A potential risk is that these molecules will accumulate in fatty tissues and pass up the food chain. This outcome is particularly troublesome given the lack of required biological testing before a new chemical is introduced into a commercial product. Even though chemical breakdown in the environment is as equally important as synthesis, it can be far more challenging. Most industrial chemicals are designed to be stable to avoid premature degradation. This same stability causes problems when molecules are released into the environment after their intended commercial life. A potential solution is to design chemicals that common bacteria in the soil or water can readily break down into innocuous substances. In this fashion, chemicals could perform their purpose in a product, but would then rapidly degrade when released into the environment, ensuring the integrity of natural systems. In order for chemists to be able to design chemicals with these properties, the precise mechanisms that bacteria use, and also the nature of the intermediates that are involved in the breakdown pathways, need to be well understood. This study takes an important step in that direction. By successfully reconstituting the biochemical machinery that is required for specific bacteria (Pseudomonas sp.) to break down the chemical phenyl acetic acid, the researchers clarified the role of an essential enzyme that performs an unprecedented chemical reaction in the biochemical pathway. In the key step of the process, the enzyme PaaABCE adds an oxygen atom in a chemical reaction known as an epoxidation. The product of this reaction is reactive, and is immediately transformed into innocuous byproducts by a series of other enzymes. At this point, the authors know all of the atoms that comprise PaaABCE, but not their arrangement in space. Therefore, the next step will be to figure out its structure. Knowing its chemical structure will allow chemists to design new synthetic catalysts to remediate soil or purify water.
Environmental Health News, 28 June 2012 ;