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Publication Abstract from PubMed

We present a comprehensive characterization of the nucleoside N-ribohydrolase (NRH) family in two model plants, Physcomitrella patens (PpNRH) and Zea mays (ZmNRH), using "in vitro" and "in planta" approaches. We identified two NRH subclasses in the plant kingdom; one preferentially targets the purine ribosides inosine and xanthosine while the other is more active towards uridine and xanthosine. Both subclasses can hydrolyze plant hormones - cytokinin ribosides. We also solved the crystal structures of two purine NRHs, PpNRH1 and ZmNRH3. Structural analyses, site-directed mutagenesis experiments, and phylogenetic studies were conducted to identify the residues responsible for the observed differences in substrate specificity between the NRH isoforms. The presence of a tyrosine at position 249 (PpNRH1 numbering) confers high hydrolase activity for purine ribosides, while an aspartate residue in this position confers high activity for uridine. Bud formation is delayed by knocking out single NRH genes in Physcomitrella, and under conditions of nitrogen shortage, PpNRH1-deficient plants cannot salvage adenosine-bound nitrogen. All PpNRH knockout plants display elevated levels of certain purine and pyrimidine ribosides and cytokinins that reflect the substrate preferences of the knocked-out enzymes. NRH enzymes thus have functions in cytokinin conversion and activation as well as in purine and pyrimidine metabolism.

Structure and function of nucleoside hydrolases from Physcomitrella and maize catalyzing hydrolysis of purine, pyrimidine and cytokinin ribosides.,Kopecna M, Blaschke H, Kopecny D, Vigouroux A, Koncitikova R, Novak O, Kotland O, Strnad M, Morera S, von Schwartzenberg K Plant Physiol. 2013 Oct 29. PMID:24170203^[1]

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