Completing the uric acid degradation pathway through phylogenetic comparison of whole genomes

Abstract

Mammals that degrade uric acid are not affected by gout or urate kidney stones. It is not fully understood how they convert uric acid into the much more soluble allantoin. Until recently, it had long been thought that urate oxidase was the only enzyme responsible for this conversion. However, detailed studies of the mechanism and regiochemistry of urate oxidation have called this assumption into question, suggesting the existence of other distinct enzymatic activities. Through phylogenetic genome comparison, we identify here two genes that share with urate oxidase a common history of loss or gain events. We show that the two proteins encoded by mouse genes catalyze two consecutive steps following urate oxidation to 5-hydroxyisourate (HIU): hydrolysis of HIU to give 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU) and decarboxylation of OHCU to give S-(+)-allantoin. Urate oxidation produces racemic allantoin on a time scale of hours, whereas the full enzymatic complement produces dextrorotatory allantoin on a time scale of seconds. The use of these enzymes in association with urate oxidase could improve the therapy of hyperuricemia.

Structural and functional analysis of PucM, a hydrolase in the ureide pathway and a member of the transthyretin-related protein family

“…This proposal is further supported by the recent findings of another HIUHase in the TRP family, MuraH (11). Our analyses raise the question of how do two totally unrelated proteins, soybean HIUHase and PucM, carry out an identical biochemical reaction?…”

“…Recently, three genes were characterized as HIUHases: a soybean (Glycine max) gene (7,8), PucM in Bacillus subtilis (10), and MuraH in mice (11). Sequence alignment has shown that the PucM and MuraH genes belong to the same family of proteins, but the third gene differs markedly from the other two in size and sequence similarity (11). Therefore, any possible relationship between these two groups remains elusive.…”

“…1.7.3.3; uricase), but recent investigations have revealed that this pathway includes two additional, distinct, chemically labile intermediates: 5-hydroxyisourate (HIU) and 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline (OHCU) (5,6). It is now generally believed that urate oxidase is responsible only for the conversion of uric acid into HIU, and a second enzyme, HIU hydrolase (HIUHase), catalyzes the hydrolysis of HIU into OHCU (7)(8)(9)(10)(11), which is then converted into allantoin via an enzyme-dependent decarboxylation reaction (Scheme 1) (11). Recently, three genes were characterized as HIUHases: a soybean (Glycine max) gene (7,8), PucM in Bacillus subtilis (10), and MuraH in mice (11).…”

“…It is now generally believed that urate oxidase is responsible only for the conversion of uric acid into HIU, and a second enzyme, HIU hydrolase (HIUHase), catalyzes the hydrolysis of HIU into OHCU (7)(8)(9)(10)(11), which is then converted into allantoin via an enzyme-dependent decarboxylation reaction (Scheme 1) (11). Recently, three genes were characterized as HIUHases: a soybean (Glycine max) gene (7,8), PucM in Bacillus subtilis (10), and MuraH in mice (11). Sequence alignment has shown that the PucM and MuraH genes belong to the same family of proteins, but the third gene differs markedly from the other two in size and sequence similarity (11).…”

Nitrogen recycling and nutritional provisioning byBlattabacterium, the cockroach endosymbiont

“…Because a cultivation-dependent approach is nearly impossible, we used bioinformatics to explore the Blattabacterium genome for uricolytic capabilities. Uricase catalyzes the first step in aerobic uric acid catabolism to allantoin (44,45), but no genes encoding a uricase were identified. A search of sequence databases for Bacteroidetes genes encoding uricases resulted in nine hits to genes encoding proteins annotated as uricase or as either hydroxyisourate hydrolase or transthyretin-like periplasmic protein.…”