Dataset Information

Biosynthesis of the ?-methylarginine residue of peptidyl nucleoside arginomycin in Streptomyces arginensis NRRL 15941.

ABSTRACT: The peptidyl nucleoside arginomycin is active against Gram-positive bacteria and fungi but displays much lower toxicity to mice than its analog blasticidin S. It features a rare amino acid, ?-methylarginine, which is attached to the deoxyhexose moiety via a 4'-aminoacyl bond. We here report cloning of the complete biosynthetic gene cluster for arginomycin from Streptomyces arginensis NRRL 15941. Among the 14 putative essential open reading frames, argM, encoding an aspartate aminotransferase (AAT), and adjacent argN, encoding an S-adenosyl methionine (SAM)-dependent methyltransferase, are coupled to catalyze arginine and yield ?-methylarginine in Escherichia coli. Purified ArgM can transfer the ?-amino group of l-arginine to ?-ketoglutaric acid to give glutamate and thereby converts l-arginine to 5-guanidino-2-oxopentanoic acid, which is methylated at the C-3 position by ArgN to form 5-guanidino-3-methyl-2-oxopentanoic acid. Iteratively, ArgM specifically catalyzes transamination from the donor l-aspartate to the resulting 5-guanidino-3-methyl-2-oxopentanoic acid, generating ?-methylarginine. The complete and concise biosynthetic pathway for the rare and bioactive amino acid revealed by this study may pave the way for the production of ?-methylarginine either by enzymatic conversion or by engineered living cells.

SUBMITTER: Feng J

PROVIDER: S-EPMC4135772 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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Biosynthesis of the β-methylarginine residue of peptidyl nucleoside arginomycin in Streptomyces arginensis NRRL 15941.

Feng Jun J Wu Jun J Gao Jie J Xia Zhigui Z Deng Zixin Z He Xinyi X

Applied and environmental microbiology 20140606 16

The peptidyl nucleoside arginomycin is active against Gram-positive bacteria and fungi but displays much lower toxicity to mice than its analog blasticidin S. It features a rare amino acid, β-methylarginine, which is attached to the deoxyhexose moiety via a 4'-aminoacyl bond. We here report cloning of the complete biosynthetic gene cluster for arginomycin from Streptomyces arginensis NRRL 15941. Among the 14 putative essential open reading frames, argM, encoding an aspartate aminotransferase (AA ...[more]

PMID: 24907335

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Project description:Type II thioesterases typically function as editing enzymes, removing acyl groups that have been misconjugated to acyl carrier proteins during polyketide secondary metabolite biosynthesis as a consequence of biosynthetic errors. Streptomyces chartreusis NRRL 3882 produces the pyrrole polyether ionophoric antibiotic, and we have identified the presence of a putative type II thioesterase-like sequence, calG, within the biosynthetic gene cluster involved in the antibiotic's synthesis. However, targeted gene mutagenesis experiments in which calG was inactivated in the organism did not lead to a decrease in calcimycin production but rather reduced the strain's production of its biosynthetic precursor, cezomycin. Results from in vitro activity assays of purified, recombinant CalG protein indicated that it was involved in the hydrolysis of cezomycin coenzyme A (cezomycin-CoA), as well as other acyl CoAs, but was not active toward 3-S-N-acetylcysteamine (SNAC; the mimic of the polyketide chain-releasing precursor). Further investigation of the enzyme's activity showed that it possessed a cezomycin-CoA hydrolysis Km of 0.67 mM and a kcat of 17.77 min-1 and was significantly inhibited by the presence of Mn2+ and Fe2+ divalent cations. Interestingly, when S. chartreusis NRRL 3882 was cultured in the presence of inorganic nitrite, NaNO2, it was observed that the production of calcimycin rather than cezomycin was promoted. Also, supplementation of S. chartreusis NRRL 3882 growth medium with the divalent cations Ca2+, Mg2+, Mn2+, and Fe2+ had a similar effect. Taken together, these observations suggest that CalG is not responsible for megasynthase polyketide precursor chain release during the synthesis of calcimycin or for retaining the catalytic efficiency of the megasynthase enzyme complex as is supposed to be the function for type II thioesterases. Rather, our results suggest that CalG is a dedicated thioesterase that prevents the accumulation of cezomycin-CoA when intracellular nitrogen is limited, an apparently new and previously unreported function of type II thioesterases.IMPORTANCE Type II thioesterases (TEIIs) are generally regarded as being responsible for removing aberrant acyl groups that block polyketide production, thereby maintaining the efficiency of the megasynthase involved in this class of secondary metabolites' biosynthesis. Specifically, this class of enzyme is believed to be involved in editing misprimed precursors, controlling initial units, providing key intermediates, and releasing final synthetic products in the biosynthesis of this class of secondary metabolites. Our results indicate that the putative TEII CalG present in the calcimycin (A23187)-producing organism Streptomyces chartreusis NRRL 3882 is not important either for the retention of catalytic efficiency of, or for the release of the product compound from, the megasynthase involved in calcimycin biosynthesis. Rather, the enzyme is involved in regulating/controlling the pool size of the calcimycin biosynthetic precursor, cezomycin, by hydrolysis of its CoA derivative. This novel function of CalG suggests a possible additional activity for enzymes belonging to the TEII protein family and promotes better understanding of the overall biosynthetic mechanisms involved in the production of this class of secondary metabolites.

Project description:Calcimycin, N-demethyl calcimycin, and cezomycin are polyether divalent cation ionophore secondary metabolites produced by Streptomyces chartreusis A thorough understanding of the organization of their encoding genes, biosynthetic pathway(s), and cation specificities is vitally important for their efficient future production and therapeutic use. So far, this has been lacking, as has information concerning any biosynthetic relationships that may exist between calcimycin and cezomycin. In this study, we observed that when a Cal- (calB1 mutant) derivative of a calcimycin-producing strain of S. chartreusis (NRRL 3882) was grown on cezomycin, calcimycin production was restored. This suggested that calcimycin synthesis may have resulted from postsynthetic modification of cezomycin rather than from a de novo process through a novel and independent biosynthetic mechanism. Systematic screening of a number of Cal-S. chartreusis mutants lacking the ability to convert cezomycin to calcimycin allowed the identification of a gene, provisionally named calC, which was involved in the conversion step. Molecular cloning and heterologous expression of the CalC protein along with its purification to homogeneity and negative-staining electron microscopy allowed the determination of its apparent molecular weight, oligomeric forms in solution, and activity. These experiments allowed us to confirm that the protein possessed ATP pyrophosphatase activity and was capable of ligating coenzyme A (CoA) with cezomycin but not 3-hydroxyanthranilic acid. The CalC protein's apparent Km and kcat for cezomycin were observed to be 190 ?M and 3.98 min-1, respectively, and it possessed the oligomeric form in solution. Our results unequivocally show that cezomycin is postsynthetically modified to calcimycin by the CalC protein through its activation of cezomycin to a CoA ester form.IMPORTANCE Calcimycin is a secondary metabolite divalent cation-ionophore that has been studied in the context of human health. However, detail is lacking with respect to both calcimycin's biosynthesis and its biochemical/biophysical properties as well as information regarding its, and its analogues', divalent cation binding specificities and other activities. Such knowledge would be useful in understanding how calcimycin and related compounds may be effective in modifying the calcium channel ion flux and might be useful in influencing the homeostasis of magnesium and manganese ions for the cure or control of human and bacterial infectious diseases. The results presented here unequivocally show that CalC protein is essential for the production of calcimycin, which is essentially a derivative of cezomycin, and allow us to propose a biosynthetic mechanism for calcimycin's production.

Dataset Information

Biosynthesis of the ?-methylarginine residue of peptidyl nucleoside arginomycin in Streptomyces arginensis NRRL 15941.

Publications

Biosynthesis of the β-methylarginine residue of peptidyl nucleoside arginomycin in Streptomyces arginensis NRRL 15941.

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