Self-sacrificial tyrosine cleavage by an Fe:Mn oxygenase for the biosynthesis of <i>para</i> -aminobenzoate in <i>Chlamydia trachomatis</i>

Abstract

Chlamydia protein associating with death domains (CADD) is involved in the biosynthesis of <i>para</i>-aminobenzoate (pABA), an essential component of the folate cofactor that is required for the survival and proliferation of the human pathogen <i>Chlamydia trachomatis</i>. The pathway used by <i>Chlamydiae</i> for pABA synthesis differs from the canonical multi-enzyme pathway used by most bacteria that relies on chorismate as a metabolic precursor. Rather, recent work showed pABA formation by CADD derives from l-tyrosine. As a member of the emerging superfamily of heme oxygenase-like diiron oxidases (HDOs), CADD was proposed to use a diiron cofactor for catalysis. However, we report maximal pABA formation by CADD occurs upon the addition of both iron and manganese, which implicates a heterobimetallic Fe:Mn cluster is the catalytically active form. Isotopic labeling experiments and proteomics studies show that CADD generates pABA from a protein-derived tyrosine (Tyr27), a residue that is ∼14 Å from the dimetal site. We propose that this self-sacrificial reaction occurs through O₂ activation by a probable Fe:Mn cluster through a radical relay mechanism that connects to the "substrate" Tyr, followed by amination and direct oxygen insertion. These results provide the molecular basis for pABA formation in <i>C. trachomatis</i>, which will inform the design of novel therapeutics.