General Structure
Antigen 85C was crystallized in its dimeric form.[3] The 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 , similar to that of chymotrypsin. By modifying 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.[3]
