FadD13 is composed of 503 amino acid residues divided into three main regions: The <scene name='69/694233/Domains/1'>N-terminal domain</scene> (residues 1-395) and <scene name='69/694233/C-terminal_domain/1'>C-terminal domain</scene> (residues 402-503) which are connected via a flexible <scene name='69/694232/Linker_section/2'>linker</scene> (residues 396-401).<ref name="Our Paper"/> Each region plays an important role in the activation of fatty acids. The large N-terminal domain has the most structural features, but it is ultimately the flexible linker that allows movement of the C-terminal domain to from the fully functioning active site (Figure 1).
FadD13 is composed of 503 amino acid residues divided into three main regions: The <scene name='69/694233/N_terminal_domain/1'>N-terminal domain</scene> (residues 1-395) and <scene name='69/694233/C-terminal_domain/2'>C-terminal domain</scene> (residues 402-503) which are connected via a flexible <scene name='69/694233/Linker_section/2'>linker</scene> represented in dark blue (residues 396-401).<ref name="Our Paper"/> Each region plays an important role in the activation of fatty acids. The large N-terminal domain has the most structural features, but it is ultimately the flexible linker that allows movement of the C-terminal domain to from the fully functioning active site (Figure 1).
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This Sandbox is Reserved from 02/09/2015, through 05/31/2016 for use in the course "CH462: Biochemistry 2" taught by Geoffrey C. Hoops at the Butler University. This reservation includes Sandbox Reserved 1051 through Sandbox Reserved 1080.
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Mycobacterium tuberculosis very-long-chain fatty acyl-CoA synthetase, also known as FadD13, is unique within its class in regards to its ability to house lipid substrates longer than itself. Most FadD class proteins exist as integral membrane proteins involved in lipid transport into the cell. FadD13 is unique structurally in that it exists as a peripheral protein on the inside of the cell membrane. This feature is key in the mechanistic basis for FadD13's activation and transport of fatty acids of length C24-C26 through the two step addition of Coenzyme A(Figure 1).[1]
FadD13 may be important in the virulence of Mycobacterium tuberculosis, the etiological agent of tuberculosis, and has emerged as possible target for novel therapeutic agents.[2]
Mechanism
Figure 1: Mechanism for the activation of fatty acids (C24-C26) by FadD13. The N terminal domain (pink) is embedded in the membrane with the arginine rich lid-loop (dark blue), while the flexile linker (black) connects the C terminal domain (green) to the rest of the enzyme. Activation requires the binding of ATP (blue) which induces structural changes that promote the binding of the fatty acid chain. Formation of an acyl-adenylate intermediate induces a 140° rotation of the C terminal domain and the binding of CoA (orange). Figure 2: Representation of the two-step reaction catalyzed by FadD13
General mechanism for the activation of fatty acids
FadD13 first activates the fatty acid through a reaction with ATP to form an acyl adenylate intermediate and release pyrophosphate. Following a conformational change of the enzyme, coenzyme A is able to bind and reaction with the acyl adenylate intermediate forming the acyl CoA product (Figure 2).
Structural basis for housing lipid substrates longer than the enzyme
The ability for FadD13 to transport and activate fatty acids of the maximum tested length C26, lies in it being a peripheral membrane protein with a hydrophobic tunnel. FadD13 is attached to the membrane via electrostatic interactions in the N-terminal domain. Of importance in the region is the arginine rich lid-loop which serves to block the transport of fatty acids into the enzyme. Once the lid-loop is opened, fatty acids may be pulled from the membrane into a hydrophobic tunnel, which is the main structural component by which fatty acids are transported from the membrane into the cell. Negatively charged residues at the active site of FadD13 are the driving factor in the attraction of the fatty acid from the membrane through the hydrophobic tunnel of the enzyme.
Structure
FadD13 is composed of 503 amino acid residues divided into three main regions: The N-terminal domain (residues 1-395) and C-terminal domain (residues 402-503) which are connected via a flexible linker represented in dark blue (residues 396-401).[1] Each region plays an important role in the activation of fatty acids. The large N-terminal domain has the most structural features, but it is ultimately the flexible linker that allows movement of the C-terminal domain to from the fully functioning active site (Figure 1).
Electrostatics
Figure Legend. Pmyol depiction of electrostatic interaction of FadD13.
The electrostatics of FadD13 as seen in (figure...) illustrate the hydrophobic and positively charged regions that compose this protein. Experimental results revealed that the peripheral FadD13 is attached to the membrane via electrostatic and hydrophobic regions located on the top portion of the N-terminal region (figure 3).[1] Of key importance in this N-terminal domain region attached to the membrane is an area of notable arginine rich residues, known as the arginine rich lid-loop.
Arginine Rich Lid-loop
The arginine rich lid loop functions to block entry of fatty acids into the hydrophobic tunnel of FadD13.This area on the top portion of the enzyme is also crucial in the association with the membrane as the positively charged arginine residues are attracted to the negative charge on the phospholipid heads.[1]
Hydrophobic Tunnel
The hydrophobic tunnel of FadD13 is essential to the transport and accommodation of very long fatty acids from the membrane into the cell. This tunnel runs through the middle of FadD13 from the arginine rich lid loop to the ATP binding site and is situated between the and alpha helices α8-α9 and parallel beta sheet β9- β14.[1]
Active Site
The active site on FadD13 is composed of two conserved regions, one of which serves as the binding site for ATP and the other for CoA. The adenine of ATP is bound to a group of six amino acids (300-305) that is structurally identically to other acyl-CoA synthetases. [1]
Disease
Mycobacterium tuberculosis is the causative agent involved in the disease tuberculosis.
Relevance
Inhibitors
Future Research
This is a sample scene created with SAT to color by Group, and another to make a transparent representation of the protein. You can make your own scenes on SAT starting from scratch or loading and editing one of these sample scenes.
↑ 1.01.11.21.31.41.5Andersson CS, Lundgren CA, Magnusdottir A, Ge C, Wieslander A, Molina DM, Hogbom M. The Mycobacterium tuberculosis Very-Long-Chain Fatty Acyl-CoA Synthetase: Structural Basis for Housing Lipid Substrates Longer than the Enzyme. Structure. 2012 May 2. PMID:22560731 doi:10.1016/j.str.2012.03.012
↑Jatana N, Jangid S, Khare G, Tyagi AK, Latha N. Molecular modeling studies of Fatty acyl-CoA synthetase (FadD13) from Mycobacterium tuberculosis--a potential target for the development of antitubercular drugs. J Mol Model. 2011 Feb;17(2):301-13. doi: 10.1007/s00894-010-0727-3. Epub 2010 May, 8. PMID:20454815 doi:https://dx.doi.org/10.1007/s00894-010-0727-3
