Progress of nitrogen-phosphorus bond biosynthesis study of naturally occurring phosphoramidates

Abstract

Naturally occurring phosphoramidates, which contain nitrogen-phosphorus (N−P) bonds, show high structure similarity with cytoplasmic carboxylates and phosphates. Phosphoramidates exhibit wide bioactivity spectrum attributed to the role as inhibitor of certain necessary enzymes in cell cycle. Three N−P bond biosynthetic pathways, which are respectively catalyzed by MccB, adenylyl sulphate: ammonia adenylyltransferase (APSAT) and Pyruvate phosphate dikinase (PPDK) homologues, are reviewed here. (1) MccB, a homologue of E1 ubiquitin ligase, catalyzed the phosphorylation of the asparagine residue of Microcin C7 precursor peptide. It consumed one molecule of ATP for the cyclization of the asparagine residue to give a succinimide. Then, the succinimidyl nitrogen atom attacked the Pα of a second ATP molecule to create an adenosine monophosphate- N -succinimide moiety. Agrocin 84, dinogunellin and phosmidosine shared identical AMP-NHR structural moiety with Microcin C7. Unfortunately, the biosynthetic gene clusters of dinogunellin and phosmidosine have not been identified yet. Agrocin 84 contains two N-P bonds, the first one linked the amino group of 2,3-dihydroxy-4-methyl-pentanamide with the phosphate group of 3′dAMP, and the second one bridged the amino group of the 3′dAMP purine ring with the phosphate group on the phosphorylated D-glucofuranosyloxy- phosphoryl. Analysis of Agrocin 84 biosynthetic gene cluster showed that agnA is homologous to mccB gene. Based on structural similarity and gene homology, it was proposed that the first N−P bond biosynthetic pathway of agrocin 84 is similar to that of Microcin C7. (2) APSAT catalyzed ammonolysis of adenosine-5′-phosphosulfate to give adenosine- 5′-phosphoramidate (AMP-NH2) and sulfate. AMP-NH2 was discovered from the extracts of Chlorella pyrenoidosa , Dictyostelium discoideum , Euglena gracilis var. bacillaris , spinach, barley and Escherichia coli . This APSAT protein was isolated from Chlorella pyrenoidosa and the biochemical characters were investigated. To eukaryotes, human Fhit (Fragile Histidine Triad) showed adenylyltransferase activity as well. It not only catalyzed the hydrolysis of diadenosine triphosphate (ApppA) to form AMP and ADP, but also catalyzed the ammonolysis of ApppA to form AMP-NH2 and ADP. In the hydrolysis of ApppA to AMP and ADP catalyzed by Fhit, first, ApppA and Mg2+ covalently bound to the 96th histidine residue of Fhit to form Fhit-AMP covalent intermediate and released ADP; then Fhit-AMP was further hydrolyzed to form AMP and Fhit. The Fhit-AMP could also be aminolyzed to give AMP-NH2. A possible mechanism for Fhit-catalysed ammonolysis involving nucleophilic attacks of NH3 to the covalent histidine-bound enzyme- nucleosidyl intermediate. (3) PPDK catalyzed the phosphorylation of pyruvate with an intermediate in which a phosphate group was loaded on the conserved histidine residue of PPDK. PPDK homologues PhtL and AgnD were proposed to catalyze the N-P bonds formation of Phaseolotoxin and Agrocin 84, respectively. The Walsh group of Harvard University have hypothesized that the Phaseolotoxin N-P bond was formed by nucleophilic attack of ornithine free amino to the phosphate group attached to the histidine residue of PhtL. Similarly, it can be assumed that the amino group of 3′dAMP purine ring attacking the phosphate group of AgnD1 (or AgnD2) histidine residue, makes the second N-P bond of Agrocin 84. This is a novel hypothesis of the biosynthesis of the N-P bonds in naturally occurring phosphoramidates, while the detailed enzymatic reactions remain to be studied further.