[FeFe] Hydrogenase
This Jmol Exploration was created using the Jmol Exploration Webpage Creator from the MSOE Center for BioMolecular Modeling.
Hydrogenase uses metal ions to split hydrogen gas, an unusual substance. It brings great promise to the greenest of green energy sources. It is stable and must be catalyzed to enter into a chemical reaction. Spite of that, an explosive chain reaction can occur if mixed with oxygen. Hydrogen gas has many advantages for green energy. For example, it can release more energy, compared to other fuels, and water. However, it also has tremendous disadvantage. The chemical reaction can't be controlled. It is very dangerous to store because it can be very explosive. Additionally, the natural gases that split hydrogen also release carbon dioxide is released.
Globular Structure
The primary structure consists of two identical polypeptide chains with 441 amino acids. The N-terminal contains 56 amino acids that form a transit peptide that guides the protein into the chloroplast where it cleaves into a motif of Val-Ala-Cys-Ala-. In addition, it contains 45 amino acids between residues Ser-284 and Val-330 that can form an external loop. The loop contributes to the electrostallic binding in the ferrodoxin-hydrogenase creation. Ferrodoxin Cn transports electrons from photosystem 1 to [FeFe]-hydrogenase so it can reduce individual atoms into the formation of divalent hydrogen.
[FeFe]-hydrogenase is a globular protein categorized known as α/β protein. That is because it contains α-helices and β-sheets along with intermingled coils. The secondary structure contains 21 a-helices with 176 residues and 17 b-sheets with 58 residues. These make up 38% and 12% of the protein. [FeFe]-hydrogenase is a homomultimer with two subunits that contain two domains which are between the active site.
Secondary structureAlso known as the H-Cluster. It is located at the interior of the protein surrounded by amino acids such as:
Pro-37, Ala-38, Thr-74, Ala-78, Cys-113, Pro-138, Met-167, Lys-172, Glu-175, Phe-234, Val-240 and Met-359.
These amino acids are hydrophobic that protect the H-cluster from solvent access. The [FeFe]-hydrogenase is only active in anaerobic cells. The Sulfur deprivation increases anaerobic conditions that increase hydrogen production.
The sub-cluster is composed of two atoms, proximal (Fep) and distal (Fed), that are coordinated by non-protein ligands with two terminal CO, a bridging CO and two terminal CN. The two Fe atoms are also bridged by the dithiomethylamine ligands.
The identification of maturation proteins were discovered in mutant strains incapable of producing H2. Requires a minimum of three auxiliary proteins:
- Two Radical-SAM enzymes (designation for a superfamily of enzymes that use a [4Fe-4S]+ cluster)
- One GTPases (large family of hydrolase enzymes that can bind and hydrolyze guanosine triphosphate)
These three auxiliary proteins can generate the active enzyme to avoid deficiency in [FeFe]-hydrogenase.
Mutations come from two genes, hydEF and hydG which are present in all organism specially in green algae.
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Maturation of hydrogenases. (n.d.). Retrieved November, 2016, from https://www.ncbi.nlm.nih.gov/pubmed/17091562
New Method Uses Bacteria to Generate Hydrogen Gas. (n.d.). Retrieved November, 2016, from https://www.wired.com/2007/11/hydrogen-bacteria/
P. (2012, September 14). The [4Fe-4S]-cluster coordination of [FeFe]-hydrogenase maturation protein HydF as revealed by EPR and HYSCORE spectroscopies. Elsevier,2149-2157. Retrieved November, 2016, from http://ac.els-cdn.com/S0005272812010274/1-s2.0-S0005272812010274-main.pdf?_tid=72876936-c153-11e6-ba73-00000aacb362&acdnat=1481647663_767ae5cbcf3c17e4b183f7f060b860e0
PDB-101: Hydrogenase. (n.d.). Retrieved November, 2016, from http://pdb101.rcsb.org/motm/111