Written by Ummulwara Qasim
The importance of nitrogenase, an enzyme responsible for the fixation of atmospheric nitrogen, is evident in many biochemical reactions in the biological systems. The ability to reduce nitrogen into ammonia is not only useful to our body for many organ systems, but also essential for the ecosystem for plant sustainability [6]. Nitrogenase also catalyzes the reaction to reduce carbon monoxide into hydrocarbons found in all organic lifeforms [5]. We consume many hydrocarbons and have ammonia running through our system, but we are still in the process of studying the source of these nutrients and molecules further. Due to the environmental changes on Earth over the past few decades, the role that nitrogenase plays in the nitrogen cycle has been impacted and disrupted by the harmful effects of global warming. In order to combat these negative impacts to the atmospheric nitrogen, scientists have come up with ways to synthesize these metalloenzymes in order to help the nitrogen fixation cycle facilitate and allow for the nitrogen cycle to occur more efficiently.
Scientists at the University of California, Irvine have been reviewing many of these methods to create biosynthetic metalloenzymes. Dr. Markus Ribbe has recently been conducting different studies in order to test for the efficiency of the metalloenzymes and further investigate different biosynthetic metalloclusters being synthesized. Metalloclusters are a type of enzyme that are composed of metalloproteins which contain a metal ion cofactor such as molybdenum or vanadium [3]. The properties of these metals play an important role for the protein in order to perform many of the catalytic reactions in different biological pathways [1]. Along with this pathway research, Dr. Ribbe’s lab has categorized a new class of proteins called radical SAM methyltransferases belonging to the family of NifB proteins [4]. NifB proteins are proteins that are essential for the nitrogen cycle in order to form nitrogenase since they are the cofactors that help assemble enzymes in the body. Methyltransferases are enzymes that interact with the chemical structure of the protein such as with nitrogenase in order to achieve a biological function for the protein [4]. This way, the protein’s expression or effectiveness can be manipulated to properly fit the situation. This new class of proteins has been found to be a part of the general function of the metalloclusters of enzymes. This discovery allows for a new platform for scientists to be able to better synthesize the metalloenzymes in order for a more effective product to be utilized in the biological system.
Dr. Ribbe’s lab will be reviewing and summarizing the progress made in unraveling this new biosynthetic mechanism and the efficiency of the new cofactor species of nitrogenase. They will be examining more closely the assembly mechanisms of two metalloclusters in particular: Mo-nitrogenase and V-nitrogenase [3]. Molybdenum and Vanadium are two metallic cofactors belonging to a homologous enzyme family. The scientists from the lab will be providing a brief explanation of the possible assembly arrangements of the two nitrogenases, and discussing the efficacy of utilizing the biosynthetic forms of these metalloenzymes.
This review can bring concrete findings to help determine if these biosynthetic metalloclusters can bring a positive impact in bringing more solutions to fixing the alterations in the nitrogen cycle, one of the many effects of global warming. Atmospheric nitrogen is heavily affected by greenhouse gases as well as the human-generated reactive nitrogen that is being produced in massive amounts due to many of the global industrial activities [2]. Metalloenzymes such as nitrogenase can potentially reduce the reactive forms of nitrogen being emitted. Analyzing possible biosynthetic mechanisms for crucial metalloenzymes can provide another option when countering the depletion of many of the important enzymes needed in the biosphere, such as nitrogenase needed for the nitrogen cycle. Dr. Ribbe’s review is expected to be published on June 2, 2016, and can be found on Annual Review of Biochemistry Volume 85. Please see http://www.annualreviews.org/catalog/pubdates.aspx for any changes.
References:
1. Douglas, CR. 2002. “Great Metalloclusters in Enzymology.” Annual Review of Biochemistry. Volume: 71.
2. Field, Scott. 2004. “Global Nitrogen Cycling Out of Control.” Environmental Health Perspectives. Volume: 112.
3. Hu, Y. Ribbe, MW. 2016. “Biosynthesis of the Metalloclusters of Nitrogenase.” Annual review of biochemistry. Volume: 85.
4. Hu, Y. Ribbe, MW. 2016. “Maturation of nitrogenase cofactor-the role of a class E radical SAM methyltransferase NifB.” Current opinion in chemical biology. Volume: 31.
5. Hu, Y. Ribbe, MW. 2016. “Nitrogenase- A Tale of Carbon Atom(s).”Angewandte Chemie (International ed. In English). Volume: 10.
6. Lee, CC. Hu, Y. Ribbe, MW. 2015. “Insights into hydrocarbon formation by nitrogenase cofactor homologs.” mBio. Volume: 6.