Defining Sequence Space and Reaction Products within the Cyanuric Acid Hydrolase (AtzD)/Barbiturase Protein Family

An unexpected vestigial protein complex reveals the evolutionary origins of an s-triazine catabolic enzyme

“…Interestingly, these enzymatic products are unstable in an aqueous environment and can undergo spontaneous reactions; allophanate decarboxylates to urea (14), whilst carbamic acid decomposes to ammonia and carbon dioxide in water (13,15). AtzD and AtzF have been overproduced in heterologous expression systems, which has allowed them to be studied biochemically (14)(15)(16)(17) and structurally (11)(12)(13)18). However, expression and purification of AtzE in a heterologous system has been challenging (1) and structural and biochemical data had not been obtained previously.…”

“…AtzD can be replaced by homologs, such as TrzD from Pseudomonas sp. strain NRRLB-12227 (56 % identity to AtzD; (16,17)). AtzF is sometimes substituted by the homologous TrzF found in Enterobacter cloacae strain 99 (70 % identity to AtzF; (14)) and AtzE has been replaced with the non-homologous biuret amidohydrolase (BiuH, a (/)8 TIM barrel cysteine hydrolase) in Rhizobium leguminasorum bv.…”

Expanding the Cyanuric Acid Hydrolase Protein Family to the Fungal Kingdom

“…A recent study found 41 homologs of known cyanuric acid hydrolase genes in publicly available sequenced genomes (11). In that study, only one eukaryotic cyanuric acid hydrolase homolog, from the green alga Micromonas sp.…”

“…Current knowledge of cyanuric acid hydrolase genes and enzymes is derived exclusively from studies with bacterial strains (8,10,11,(14)(15)(16). A recent study found 41 homologs of known cyanuric acid hydrolase genes in publicly available sequenced genomes (11).…”

“…These bacteria transform cyanuric acid to 3 mol each of ammonia and carbon dioxide (7) in a three-enzyme hydrolytic pathway. The pathway begins with cleavage of the s-triazine ring by the enzyme cyanuric acid hydrolase, which produces biuret (8)(9)(10)(11). Subsequently, biuret undergoes enzymatic hydrolysis with the release of ammonia by biuret hydrolase (9,12), and the other product, allophanate, is hydrolyzed by allophanate hydrolase (13) to produce 2 mol of ammonia and carbon dioxide, respectively.…”