Sandbox Reserved 911: Difference between revisions

Crystal structures of FAAH show that the enzyme is a <scene name='57/573125/2vya/1'>homodimer</scene> with <scene name='57/573125/2vya/3'>PF-750 inhibitor</scene> in solution, with each subunit having a mass of 63 kD. The protein's <scene name='57/573125/2vya/8'>twisted Beta sheet core</scene> of 11 strands is surrounded by 24 alpha helices. The enzyme is embedded in the cell <scene name='57/573125/2vya/5'>membrane</scene> to catch the lipid signaling molecules that can diffuse through membranes. The FAAH structure shows an entry channel leading from the lipid bilayer to the enzyme's active site, providing a path for endocannabinoids to enter the hydrolase. This entry channel is amphipathic to accommodate the entire lipid signaling molecule. Hydrophobic amino acid residues interact with the lipid signaling molecules' nonpolar tails, while charged R486 and D403 residues in the entry channel accommodate the polar head groups. In addition, FAAH possesses a channel leading from the active site to the cell's cytoplasm, allowing the release of polar compounds released from lipid cleavage and the entry of water molecules necessary for the FAAH mechanism to proceed. (IMT5) This hydrolase has a membrane binding cap, a <scene name='57/573125/2vya/7'>helix-turn-helix motif</scene> consisting of alpha helices 18 and 19. These helices present hydrophobic amino acid residues that help FAAH interact with the hydrophobic region of the lipid bilayer. (IMT5) Different inhibitors have been designed to learn more about species selectivity (2VYA) and binding flexibility (2WJ2).

Mutagenesis and inhibitor studies have shown that FAAH has a <scene name='57/573125/2vya/6'>Ser-Ser-Lys catalytic triad</scene>, consisting of Ser241, Ser217, and Lys142. Ser-Ser-Lys catalytic triads are not often seen in hydrolases, making FAAH an enzyme of interest for additional research to better determine how proteins with this catalytic triad function. Ser241 acts as the catalytic nucleophile for the cleavage of amide bonds. (IMT5) Inhibitors are able to inactivate the catalytic triad by providing a substrate containing a leaving group, such as aniline, that is a more favorable leaving group than the Ser241 hydroxyl group.  With the serine bound to the carbonyl carbon, FAAH is no longer able to accommodate any more substrates (2VYA). FAAH also requires two water molecules in its active site to properly position and cleave amide bonds. One water molecule (W1) deacylates the substrate, and the other (W2) helps coordinate W1 through the catalytic K142. (3LJ6)