PhzS

PhzS is a flavin-dependent monooxygenase encoded by the phzS gene within the phenazine biosynthesis gene cluster of certain Pseudomonas species, most notably Pseudomonas aeruginosa. In the late steps of phenazine production, PhzS catalyzes the oxidation and hydroxylation of the methylated phenazine intermediate 5-methyl-phenazine-1-carboxylate (5-Me-PCA) to form pyocyanin, using FAD as a cofactor and NAD(P)H as an electron donor. This reaction occurs downstream of PhzM, which converts phenazine-1-carboxylate to 5-Me-PCA, linking core phenazine synthesis to the production of pyocyanin.

The activity of PhzS is integral to the generation of pyocyanin, a blue-green pigment and redox-active compound that can generate reactive oxygen species and influence host-pathogen interactions during infection. Genetic studies show that mutants lacking phzS produce little or no pyocyanin despite the continued synthesis of other phenazine intermediates, whereas overexpression can enhance pyocyanin levels. PhzS homologs are found in related Pseudomonas species and contribute to phenazine diversification in those strains.

Biochemically, PhzS has been the subject of biochemical and structural analyses to understand cofactor binding, substrate recognition, and the mechanistic details of its monooxygenase activity. In the broader context of secondary metabolism, PhzS exemplifies how specific enzymatic steps redirect phenazine biosynthesis toward particular end products, impacting microbial physiology and virulence.