Ergot alkaloids are toxins and important pharmaceuticals that are produced biotechnologically on an industrial scale. The first committed step of ergot alkaloid biosynthesis is catalyzed by dimethylallyl tryptophan synthase (DMATS; EC 2.5.1.34). Orthologs of DMATS are found in many fungal genomes. We report here the x-ray structure of DMATS, determined at a resolution of 1.76 Å. A complex of DMATS from Aspergillus fumigatus with its aromatic substrate L-tryptophan and with an analogue of its isoprenoid substrate dimethylallyl diphosphate reveals the structural basis of this enzyme-catalyzed Friedel-Crafts reaction, which shows strict regiospecificity for position 4 of the indole nucleus of tryptophan as well as unusual independence of the presence of Mg 2؉ ions. The 3D structure of DMATS belongs to a rare /␣ barrel fold, called prenyltransferase barrel, that was recently discovered in a small group of bacterial enzymes with no sequence similarity to DMATS. These bacterial enzymes catalyze the prenylation of aromatic substrates in the biosynthesis of secondary metabolites (i.e., a reaction similar to that of DMATS).EC 2.5.1.34 ͉ ergot alkaloids ͉ PT barrel ͉ ABBA prenyltransferase
Aurachins are quinoline alkaloids isolated from the myxobacterium Stigmatella aurantiaca. They are substituted with an isoprenoid side chain and act as potent inhibitors in the electron transport chain. A biosynthetic gene cluster that contains at least five genes (auaA-auaE) has been identified for aurachin biosynthesis. In this study, auaA, the gene encoding a putative prenyltransferase of 326 amino acids, was cloned and overexpressed in Escherichia coli. Biochemical investigations showed that AuaA catalyzes the prenylation of 2-methyl-4-hydroxyquinoline in the presence of farnesyl diphosphate (FPP), thereby resulting in the formation of aurachin D. The hydroxyl group at position C4 of the quinoline ring is essential for an acceptance by AuaA; this was concluded by testing 18 quinoline derivatives or analogues with AuaA and FPP. (1) H NMR and HR-EI-MS analyses of six isolated enzyme products revealed the presence of a farnesyl moiety at position C3 of the quinoline ring. K(M) values of 43 and 270 μM were determined for FPP and 2-methyl-4-hydroxyquinoline, respectively. Like other known membrane-bound prenyltransferases, the reaction catalyzed by AuaA is dependent on the presence of metal ions such as Mg(2+) , Mn(2+) and Co(2+) , although no typical (N/D)DXXD binding motif was found in the sequence.
Background: Dimethylallyl tryptophan synthase FgaPT2 catalyzes in nature the C 4 -prenylation of indole ring. Results: FgaPT2 also catalyzes in vitro a regular C 3 -prenylation of L-tyrosine; its mutant FgaPT2_K174F showed a much higher catalytic activity toward L-tyrosine than L-tryptophan. Conclusion: Single mutation on the key amino acid switches the tryptophan C 4 -prenyltransferase to a tyrosine C 3 -prenylating enzyme. Significance: The first L-tyrosine C 3 -prenylating enzyme was created by molecular modeling-guided mutagenesis.
The aim of study was to determine the effect of selected cultivation operations, such as nitrogenous fertilization (60, 90 kg N/ha), row spacing (62, 82, 102 cm), compaction of soil with wheels of farm aggregates (the numbers of passing 2×, 5×, 8×), on quality changes of two potato varieties (Irga and Ekra). The total protein content in the tubers of the tested potato varieties increased with the increase of the nitrogenous fertilization (90 kg N/ha). Genotype features of the tested potato tubers define the amino acid limiting the protein biological value (CS) to be leucine in Irga variety and isoleucine in Ekra variety. It is also genotype that influences the second limiting amino acid. It is the sum of sulphuric amino acids (Cys + Met) in respect to Irga variety and valine in respect to Ekra variety. The dose of 90 kg N/ha decreases the protein biological value (EAAI) of the tubers of Ekra variety, which is high in starch.Keywords: potato; tuber; total protein; biological value of protein; amino acids; nitrogen fertilization; row spacing; soil compaction Protein content in tubers is an important element of the evaluation of potato quality. Although when compared to other crop plants, potatoes contain a small amount of protein (2.0-2.5% f.m.), they are an important element of human and animal diet, due to high biological value of protein -very good amino acid composition (Ciećko et al. 1999). Potato protein is plant protein of high value for both humans and animals. Potato varieties are characterised by differentiated, genetically conditioned predisposition to protein accumulation in tubers. However, similarly to most quality characteristics, protein content can be modified by various factors, such as environment, soil and tillage (Mazurczyk and Lis 1999). The basic protein components are amino acids, which, similarly to nucleic acids, take part in all intracellular processes in living organisms. The amino acid composition of proteins is important from the nutrition point of view. The amino acid composition determination acids (exogenous), namely tryptophan, phenylalanine, lysine, treonine, methionine, leucine and valine, are valuable. These amino acids are necessary for all types of the examined animals. However, a rigid set of amino acids necessary for all animals cannot be applied because some of them may require specifically a certain type of an amino acid. The analysis of the amino acid composition of the potato protein makes it possible to classify the protein as full-value, as it contains a high amount of the essential amino acids, particularly lysine (Wieczer and Gonczarik 1977). MATERIAL AND METHODSThe experimental material consisted of the tubers of two varieties: edible Irga and industrial Ekra. A field experiment was carried out in the vegetation seasons of 1997-1999 at the Experimental Farm Station, Zawady and on the experimental field of the Department of Soil Cultivation and Plant Growing, Plant Production Institute of the University of Podlasie in Siedlce. The experiment was planned in...
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