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Publication Abstract from PubMed

A recently discovered ornithine-ammonia cycle (OAC) serves as a conduit in the nitrogen storage-and-remobilization machinery in cyanobacteria. The OAC involves an arginine-catabolic reaction catalyzed by the arginine dihydrolase ArgZ whose catalytic mechanism is unknown. Here, we determined the crystal structures at 1.2-3.0 A of unliganded ArgZ from the cyanobacterium Synechocystis sp. PCC6803 and of ArgZ complexed with its substrate arginine, a covalently linked reaction intermediate, or the reaction product ornithine. The structures reveal that a key residue, Asn(71), in the ArgZ active center, functions as the determinant distinguishing ArgZ from other members of the guanidino group-modifying enzyme superfamily. The structures, along with biochemical evidence from enzymatic assays coupled with electrospray ionization MS (ESI-MS) techniques, further suggest that ArgZ-catalyzed conversion of arginine to ornithine, ammonia, and carbon dioxide by ArgZ consists of two successive cycles of amine hydrolysis. Finally, we show that arginine dihydrolases are broadly distributed among bacteria and metazoan, suggesting that the OAC may be frequently used for redistribution of nitrogen from arginine catabolism or nitrogen fixation.

Crystal structures and biochemical analyses of the bacterial arginine dihydrolase ArgZ suggests a "bond-rotation" catalytic mechanism.,Zhuang N, Zhang H, Li L, Wu X, Yang C, Zhang Y J Biol Chem. 2019 Dec 30. pii: RA119.011752. doi: 10.1074/jbc.RA119.011752. PMID:31914412^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.