The Homogentisate Pathway: a Central Catabolic Pathway Involved in the Degradation of l -Phenylalanine, l -Tyrosine, and 3-Hydroxyphenylacetate in Pseudomonas putida

Abstract

Pseudomonas putida metabolizes Phe and Tyr through a peripheral pathway involving hydroxylation of Phe to Tyr (PhhAB), conversion of Tyr into 4-hydroxyphenylpyruvate (TyrB), and formation of homogentisate (Hpd) as the central intermediate. Homogentisate is then catabolized by a central catabolic pathway that involves three enzymes, homogentisate dioxygenase (HmgA), fumarylacetoacetate hydrolase (HmgB), and maleylacetoacetate isomerase (HmgC), finally yielding fumarate and acetoacetate. Whereas the phh, tyr, and hpd genes are not linked in the P. putida genome, the hmgABC genes appear to form a single transcriptional unit. Gel retardation assays and lacZ translational fusion experiments have shown that hmgR encodes a specific repressor that controls the inducible expression of the divergently transcribed hmgABC catabolic genes, and homogentisate is the inducer molecule. Footprinting analysis revealed that HmgR protects a region in the Phmg promoter that spans a 17-bp palindromic motif and an external direct repetition from position ؊16 to position 29 with respect to the transcription start site. The HmgR protein is thus the first IclR-type regulator that acts as a repressor of an aromatic catabolic pathway. We engineered a broad-host-range mobilizable catabolic cassette harboring the hmgABC, hpd, and tyrB genes that allows heterologous bacteria to use Tyr as a unique carbon and energy source. Remarkably, we show here that the catabolism of 3-hydroxyphenylacetate in P. putida U funnels also into the homogentisate central pathway, revealing that the hmg cluster is a key catabolic trait for biodegradation of a small number of aromatic compounds.

Structure of Phenylalanine Hydroxylase from Colwellia psychrerythraea 34H, a Monomeric Cold Active Enzyme with Local Flexibility around the Active Site and High Overall Stability

“…4-Hydroxyphenylpyruvate is then further oxidized to homogentisic acid (65). The fact that C. psychrerythraea lacks an ortholog of homogentisate dioxygenase catalyzing the oxidation of homogentisic acid to 4-maleylacetoacetate, a step needed for the complete oxidation of L-Phe to carbon dioxide and water (65), further supports the hypothesis that PAH is not involved in catabolism but in specialized synthesis of metabolites derived from L-Phe and L-Tyr in C. psychrerythraea.…”

Inactivation of the hmgA gene of Pseudomonas aeruginosa leads to pyomelanin hyperproduction, stress resistance and increased persistence in chronic lung infection

“…This pathway involves three enzymes: homogentisate dioxygenase, mal- eylacetoacetate isomerase and fumarylacetoacetate hydrolase. The genes encoding these enzymes appear to form a single transcriptional unit (Arias-Barrau et al, 2004). In the P. aeruginosa PA14 and PAO1 genomes, the genes hmgA, fahA and maiA (putatively encoding these three enzymes) seem to form an operon as well (Fig.…”

“…These results showed that the main pigment molecule was a derivative of homogentisic acid. It is interesting to note that this structure corresponds to the dehydrogenated (oxidized) form of homogentisic acid, the main precursor of melanin in other micro-organisms such as Pseudomonas putida, Vibrio cholerae, Burkholderia cenocepacia and Shewanella colwelliana (Arias- Barrau et al, 2004;Coon et al, 1994;Kotob et al, 1995;Kovach et al, 1995). Thus, the pigment produced by the hmgA mutant will be considered here as a pyomelanin.…”

3-Hydroxyphenylpropionate and Phenylpropionate Are Synergistic Activators of the MhpR Transcriptional Regulator from Escherichia coli

“…This agrees with the narrow effector specificity displayed by other members of the IclR family, with the unique exception of the TtgV regulator, which recognizes a wide range of structurally different effectors (40). The aromatic compounds were tested at 1 mM, as it is generally assumed that at this concentration these molecules can diffuse across biological membranes, making transport theoretically unnecessary (14,(41)(42)(43)(44)(45). Nevertheless, we cannot rule out that the absence of induction could be because of the inability of these compounds to enter the cell.…”