Sulfide quinone oxidoreductase: Difference between revisions

In PDB, this structure is marked as 6OI5 and is noted as the crystal structure of human sulfide quinone oxidoreductase. This enzyme is made up of two different amino acid chains. It contains the ligand, flavin-adenine dinucleotide (FAD). The FAD is noncovalently connected to the main subunit, and it is in the oxidized state waiting to be reduced (Jackson et al., 2019). In this structure specifically, one residue was modified into s-mercaptocysteine. This modified residue is considered L-type linking and is a potential drug target (Bank, R. P. D., 2020). In humans, the SQOR is made of two tandem Rossmann folds, and a C-terminal made up of two helices. Rossmann folds are composed of six beta sheets that are arranged parallel to one another with alpha helices connecting the first three strands (Jackson et al., 2019). The C-terminal extends outward from the main body of the enzyme, and is amphipathic, containing both hydrophobic and hydrophilic portions within the enzyme. The <scene name='88/881543/Hydrophobic_regions_-1/1'>hydrophobic region</scene> of the protruding C-terminal faces out from the membrane. Following that C-terminal, a penultimate helix arises and is very hydrophobic. It contains 16 hydrophobic residues, 11 of which are facing away from the membrane. The nonpolar residues on this penultimate helix are most tyrosines and methionines, and they face towards a cavity, indicating a binding location for coenzyme Q (Jackson et al., 2019). Due to the hydrophobic areas making contact to the inner areas of the membrane, the enzyme would be able to make its way towards coenzyme Q and pass off electrons to it. SQOR contains an indent that is electropositive, which will be the location for sulfane sulfur acceptors to bind. Within the middle of the indent, there is an opening just large enough to give access to the one of the reactive cysteine residues. There is a hydrogen sulfide oxidizing site which connects to a hydrophilic pocket, or tunnel, leading to the location where coenzyme Q will eventually bind (Jackson et al., 2019). Chain A is composed of alpha helices, beta sheets and has numerous binding sites. Chain A also contains many FAD-binding spots. A disulfide bridge connects the positions 161 to 339, or 201 to 379, also denoted by PDB, together (Bank, R. P. D., 2020). The spacing between the two cysteine active sites makes strong bridging between the two. The positions of the disulfide bonds are Cys201 and Cys379. Chain B is very much identical to Chain A in that it contains a <scene name='88/881543/Disulfide_bridge-1/4'>disulfide</scene> bridge at the positions Cys201 and Cys379 (Landry et al., 2019). Chain B is also made up of alpha helices and beta sheets. It is very much identical to Chain A in that it has a disulfide bridge at the same residues (Bank, 2020). The resolution of sulfide quinone oxidoreductase is 2.81 angstroms, and the sequence is 418 residues in length (Bank, R. P. D., 2020). The surface of SQOR that is facing the membrane is characterized by different charges and properties (Jackson et al., 2019). The surface that is facing towards the cellular matrix contains hydrophobic areas, as well as the hydrophobic coenzyme Q binding pocket. The surface facing the cellular matrix also has a very large positive charge which interacts with the phospholipid bilayer, which is negative. The other side of SQOR contains a large negative surface, where one of the Rossmann folds is located and where the electropositive divet is located (Jackson et al., 2019).