Chemical basis of nitrogen recovery through the ureide pathway: formation and hydrolysis of S-ureidoglycine in plants and bacteria.
While some organisms, including humans, eliminate oxidized purines to get rid of excess nitrogen, for many others the recovery of the purine ring nitrogen is vital. In the so-called ureide pathway, nitrogen is released as ammonia from allantoate through a series of reactions starting with allantoate amidohydrolase (AAH), a manganese-dependent enzyme found in plants and bacteria. We report NMR evidence that the true product of the AAH reaction is S-ureidoglycine, a nonstandard alpha-amino acid that spontaneously releases ammonia in vitro. Using gene proximity and logical genome analysis, we identified a candidate gene (ylbA) for S-ureidoglycine metabolism. The proteins encoded by Escherichia coli and Arabidopsis thaliana genes catalyze the manganese-dependent release of ammonia through hydrolysis of S-ureidoglycine. Hydrolysis then inverts the configuration and yields S-ureidoglycolate. S-Ureidoglycine aminohydrolase (UGHY) is cytosolic in bacteria, whereas in plants it is localized, like allantoate amidohydrolase, in the endoplasmic reticulum. These findings strengthen the basis for the known sensitivity of the ureide pathway to Mn availability and suggest a further rationale for the active transport of Mn in the endoplasmic reticulum of plant cells.
Serventi
Fabio
F
Dipartimento di Biochimica e Biologia Molecolare, Università di Parma, 43100 Parma, Italy.
Ramazzina
Ileana
I
Lamberto
Ilaria
I
Puggioni
Vincenzo
V
Gatti
Rita
R
Percudani
Riccardo
R
D000595:Amino Acid Sequence; D000619:Aminohydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000201:enzymology; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005998:Glycine / Q000031:analogs & derivatives* / Q000378:metabolism; D006868:Hydrolysis; D008345:Manganese / Q000378:metabolism*; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000378:metabolism*; D017433:Protein Structure, Secondary; D014508:Urea / Q000031:analogs & derivatives* / Q000378:metabolism; D014512:Ureohydrolases / Q000378:metabolism*
D029681:Arabidopsis Proteins; D029968:Escherichia coli Proteins; C549215:ureidoglycine; D008345:Manganese; D014508:Urea; D014512:Ureohydrolases; C019657:allantoate amidohydrolase; D000619:Aminohydrolases; C549216:YlbA protein, E coli; C546345:ureidoglycine aminohydrolase, Arabidopsis; D009584:Nitrogen; D005998:Glycine