Evolution: the newly-found bacterial role: nitrogen (Evolution)

by David Turell @, Saturday, April 20, 2019, 02:07 (154 days ago) @ David Turell

Nitrogen is most of the atmosphere but is rare in the ground and is a major molecule in many protein molecules. Bacteria have a major role in fixing the nitrogen into the ground where it can be used by living organisms:

https://phys.org/news/2019-04-fuel-cells-bacteria.html

"The exchange of nitrogen between the atmosphere and organic matter is crucial for life on Earth because nitrogen is a major component of essential molecules such as proteins and DNA. One major route for this exchange, discovered only in the 1990s, is the anammox pathway found in certain bacteria. It proceeds via hydrazine, a highly reactive substance used by humans as a rocket fuel. Researchers now describe the structure of the enzyme performing the last step in this process: turning hydrazine into nitrogen gas and harvesting the energy set free in this way. The results, which were just published in Science Advances, show an unprecedented network of heme groups for handling the large number of electrons released during the chemical conversion.

"A number of bacteria perform such conversions and contribute to the biochemical nitrogen cycle (image) by producing more reactive forms of nitrogen.

"In the 1990s, scientists discovered a bacterial process called anaerobic ammonium oxidation (anammox). "We now believe this process is responsible for 30 to 70 percent of the yearly nitrogen removal from the oceans," explains Thomas Barends,...."Due to this characteristic, anammox bacteria are used in sustainable wastewater treatment all over the world," Cornelia Welte of Radboud University adds. During this process, bacteria convert nitrites and ammonia into dinitrogen (N2) and water, while generating energy for the cell. The molecule hydrazine is produced in an intermediate step. Hydrazine is a common component of rocket fuel, but its use by bacteria as a metabolic fuel is rather exotic—and surprising in living organisms because of its high toxicity. Welte: "So far, hydrazine has only been found in anammox and not in other bacteria." Until recently, little was known about how these bacteria harness the energy released during the hydrazine conversion.

" Previously the research group and their collaborators have described the structures of the enzymes hydrazine synthase and hydroxylamine oxidoreductase. The researchers now further unravel the anammox puzzle by describing the crystal structure of hydrazine dehydrogenase, the enzyme involved in the conversion of toxic hydrazine to harmless dinitrogen gas. "Both the use of hydrazine as well as the structure of hydrazine dehydrogenase are quite unique, making it important to uncover the biological process in detail," Welte explains.

***

"'One could compare the HDH complex to a fuel cell with electrical outlets that only fit certain types of plugs," says Thomas Barends, describing the structure and mechanism of HDH. The 'fuel' hydrazine enters the protein complex through a channel on the outside. The enzyme then catalyzes the conversion of hydrazine into nitrogen gas through an unprecedentedly large network of 192 heme groups. Then the electrons are carried to other parts of the bacterium, like the transfer of current to electrical consumers. These consumers then generate the cell's energy.

"'We are now working on finding the protein that takes up the electrons stored in the heme network," says Mohd Akram, postdoc in the Barends group and first author of the paper. From the structure they observed they expect that only small proteins can enter the complex, take up the electrons in a hollow space inside, and leave again. Selecting which proteins can access the electrons may help ensure the electrons are brought to the right place to be used for energy generation in the cell. "

Comment: Another very important process bacteria must produce for life to exist. Since it uses a strange toxic hydrazine molecule the origin of this process must provide protection for the producing bacteria and must invent two very complex enzymes. Why did these bacteria develop this process, which is not necessary for their survival? Good engineering by God? Not by chance.


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