| 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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Background
The antigen 85 (ag85) complex in Mycobacterium tuberculosis is composed of three intracellular membrane proteins: ag85A, B, and C. The ag85 complex is a major component of the cell wall, with each protein catalyzing the transfer of important cell wall constituents into the membrane. [1] Ag85C is of particular interest due to its transfer of mycolic acids, which are major components in determining cell wall integrity. By targeting this mycoloyltransferase activity, inhibition of ag85C offers potential for cell wall disruption and subsequent antibiotic targeting for normally drug-resistant mycotaberia tuberculosis. [2]
Structure
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General Structure
Antigen 85C was crystallized in its dimeric form.[1] The secondary structures shown in the monomeric form are composed of helices with one interwoven beta sheet. Due to its accommodation of large fatty acid chain substrates and its incorporation into a complex with Antigen85B and A, the binding pocket is not defined past the active site residues.
Enzymatic Activity
Mutagenesis studies have confirmed the Ag85C functions through a Glu-His-Ser Catalytic Triad, similar to that of chymotrypsin. By modified each of the catalytic residues separately testing the enzyme’s relative activity, it has been shown that mutation of any one of these residues dramatically reduces activity (Figure #). The S124 alcohol’s nucleophilicity is inductively strengthened through H260 and E224, which allows S124 to hydrolyze trehalose 6, 6’-dimycolate. The formation of the functional catalytic triad relies on upon Van der Waals interaction between C209 and the peptide bond between L232 and T231. This interaction results in a kinked conformation of the α9 helix, which promotes that activity of the catalytic triad. As a result, Ag85C, a mycolyl transferase, can facilitate the modification of trehalose monomycolates to trehalose dimycolates, which are then transported to the bacterial cell wall.
Methods of Inhibition
alpha 9 helix yalready know
Inhibitors
Mutations
Structural Changes
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.
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References
- ↑ Ronning DR, Klabunde T, Besra GS, Vissa VD, Belisle JT, Sacchettini JC. Crystal structure of the secreted form of antigen 85C reveals potential targets for mycobacterial drugs and vaccines. Nat Struct Biol. 2000 Feb;7(2):141-6. PMID:10655617 doi:10.1038/72413
- ↑ Jackson M, Raynaud C, Laneelle MA, Guilhot C, Laurent-Winter C, Ensergueix D, Gicquel B, Daffe M. Inactivation of the antigen 85C gene profoundly affects the mycolate content and alters the permeability of the Mycobacterium tuberculosis cell envelope. Mol Microbiol. 1999 Mar;31(5):1573-87. PMID:10200974
