The PA4204 gene encodes a periplasmic gluconolactonase (PpgL) which is important for fitness of Pseudomonas aeruginosa.

In Pseudomonas aeruginosa, the PA4204 gene encodes a protein with a signal peptide and a
COG2706 domain of the type present in 3-carboxy-cis,cis-muconate lactonizing enzymes. A
molecular model based on the structure of the Escherichia coli YbhE phosphogluconate
lactonizing enzyme shows that the enzyme has a beta-propeller ('doughnut') structure and a
central active site comprising one histidine, one glutamic acid and two arginines. Inactivation of
the P. aeruginosa PA4204 gene had profound phenotypic effects, resulting in slowly growing
small colonies which frequently gave rise to larger colonies. The small colonies did not produce
pyocyanin, produced reduced amounts of N-acylhomoserine lactones, and had extremely low
levels of 2-alkyl-4-quinolones (AQs), while the larger colonies produced pyocyanin and higher
amounts of AQs, including the pseudomonas quinolone signal (PQS), compared with the wildtype
strain. Mutagenesis of His 182 in PA4204 resulted in the inability of this protein to restore
pyocyanin production in the PA4204 isogenic mutant, suggesting that this enzyme may share an
active site with other lactonizing enzymes. The protein with signal peptide was expressed as a
His fusion in E. coli and purified. Two forms were observed, suggesting that the protein is
translocated. The purified enzyme cleaved (S)-5-oxo-2-tetrahydrofurancarboxylic acid and Dglucono-
d-lactone, demonstrating lactonase activity. Decreased expression of the cytoplasmic
phosphogluconolactonase gene (pgl) was observed in the small-colony mutant, and the mutant
could not grow in the presence of mannitol or gluconate, suggesting functions in the detoxification
of a gluconolactone and in sugar metabolism.