Synthesis of the sulfur amino acids: cysteine and methionine

This review will assess new features reported for the molecular and biochemical aspects of cysteine and methionine biosynthesis in Arabidopsis thaliana with regards to early published data from other taxa including crop plants and bacteria (Escherichia coli as a model). By contrast to bacteria and fungi, plant cells present a complex organization, in which the sulfur network takes place in multiple sites. Particularly, the impact of sulfur amino-acid biosynthesis compartmentalization will be addressed in respect to localization of sulfur reduction. To this end, the review will focus on regulation of sulfate reduction by synthesis of cysteine through the cysteine synthase complex and the synthesis of methionine and its derivatives. Finally, regulatory aspects of sulfur amino-acid biosynthesis will be explored with regards to interlacing processes such as photosynthesis, carbon and nitrogen assimilation.     

Cyanamide mediated syntheses of peptides containing histidine and hydrophobic amino acids

Summary Using the model of a primitive earth evaporation pond, the synthesis of three histidyl peptides in yields of up to 11% was demonstrated when aqueous solutions of histidine, leucine, ATP, cyanamide, and MgCl₂ were evaporated and heated for 24 h at 80°C. In addition, peptides were formed in yields of up to 56%, 35%, and 21%, respectively for phenylalanine, leucine, and alanine when aqueous solutions of the appropriate amino acid were evaporated and heated with cyanamide and one or more of the following components: ATP, AMP, 4-amino-5-imidazole carboxamide, or MgCl₂. The greatest peptide yield occurred at pH 3. But peptide formation was demonstrated for a system of Leu, cyanamide, and MgCl₂ adjusted to pH 7 with NH₄OH.Peptide synthesis was also studied in the presence of CaCl₂, ZnCl₂, different adenosine nucleotides, and UTP to compare their effects on peptide synthesis. The optimum conditions for cyanamide mediated peptide synthesis were also studied in terms of pH, reaction time, reaction temperature, and cyanamide concentration. The major side product in nearly all reactions studied appears to be an amino acid-cyanamide adduct. Peptides were analyzed and identified by thin layer chromatography, acid hydrolysis, and enzymatic degradation.     

Novel and expanded jadomycins incorporating non-proteogenic amino acids

Jadomycin B is a secondary metabolite produced, in response to stress, by Streptomyces venezuelae ISP5230 grown in nutrient-deprived media. We present definitive electrospray ionization mass spectrometry data identifying a series of novel jadomycins with non-proteogenic amino acids incorporated into the oxazolone ring of the secondary metabolite, and strengthening evidence for the existence of an aldimine intermediate in the biosynthetic pathway. We also demonstrate that the size of the oxazolone ring can be expanded by incorporating beta-amino acids.     

Metalloporphyrins and molecular complexes of amino acids with porphyrins in juvenile volcanic ash

In samples of juvenile ash of the volcano Tjatja, USSR (that erupted in 1973) metalloporphyrins were found. With respect to the fluorescence spectra free bases of the compounds were close to the pigments that formed in abiogenic synthesis experiments (predominance of long-wave length fluorescence band). The pigments detected occurred in the ash as molecular complexes with amino acids which seem to be of abiogenic origin. These findings are of interest in terms of exploration of the processes of chemical evolution and emergence of life on the Earth.     

Metalloporphyrins and molecular complexes of amino acids with porphyrins in juvenile volcanic ash

In samples of juvenile ash of the volcano Tjatja, USSR (that erupted in 1973) metalloporphyrins were found. With respect to the fluorescence spectra free bases of the compounds were close to the pigments that formed in abiogenic synthesis experiments (predominance of long-wave length fluorescence band). The pigments detected occurred in the ash as molecular complexes with amino acids which seem to be a abiogenic origin. These findings are of interest in terms of exploration of the processes of chemical evolution and emergence of life on the Earth.     

Characterization of the amino acids involved in substrate specificity of methionine sulfoxide reductase A

Methionine sulfoxide reductases (Msrs) are ubiquitous enzymes that catalyze the thioredoxin-dependent reduction of methionine sulfoxide (MetSO) back to methionine. In vivo, Msrs are essential in protecting cells against oxidative damages on proteins and in the virulence of some bacteria. There exists two structurally unrelated classes of Msrs. MsrAs are stereo-specific toward the S epimer on the sulfur of the sulfoxide, whereas MsrBs are specific toward the R isomer. Both classes of Msrs display a similar catalytic mechanism of sulfoxide reduction by thiols via the sulfenic acid chemistry and a better affinity for protein-bound MetSO than for free MetSO. Recently, the role of the amino acids implicated in the catalysis of the reductase step of Neisseria meningitidis MsrA was determined. In the present study, the invariant amino acids potentially involved in substrate binding, i.e. Phe-52, Trp-53, Asp-129, His-186, Tyr-189, and Tyr-197, were substituted. The catalytic parameters under steady-state conditions and of the reductase step of the mutated MsrAs were determined and compared with those of the wild type. Altogether, the results support the presence of at least two binding subsites. The first one, whose contribution is major in the efficiency of the reductase step and in which the epsilon-methyl group of MetSO binds, is the hydrophobic pocket formed by Phe-52 and Trp-53, the position of the indole ring being stabilized by interactions with His-186 and Tyr-189. The second subsite composed of Asp-129 and Tyr-197 contributes to the binding of the main chain of the substrate but to a lesser extent.     

Preparation and properties of Fe3+-amino acid complexes: Crystalline complexes with aliphatic amino acids

Crystalline complexes of Fe³⁺ and several aliphatic amino acids have been prepared. All have a basic molecular constitution [Fe[AA]₂H₂O]₃O (ClO₄)₇, as determined by optical, magnetic, and Mössbauer measurements. The physical properties of these compounds display a marked similarity to those of ferritin.     

Discovering the interaction propensities of amino acids and nucleotides from protein-RNA complexes

With the availability of many genome sequences, the mining of biological data is attracting much attention, most of it limited to the sequences of macromolecules. Sequence data are easy to analyze as they can be treated as strings of characters, whereas the structure of a macromolecule is much more complex. We developed a set of algorithms to analyze the structures of protein-RNA complexes at the atomic level and used them to analyze protein-RNA interactions using structural data on 51 protein-RNA complexes. The analysis revealed, among other things, that: (1) polar and charged amino acids have a strong tendency to interact with nucleotides, (2) arginine and asparagine tend to hydrogen bond with uracil, and (3) histidine favors uracil in water-mediated bonding with RNA. We analyzed a large set of structural data of protein-RNA complexes involving water-mediated hydrogen bonds as well as direct hydrogen bonds. The interaction patterns discovered from the analysis provide useful information for predicting the structure of RNA that binds proteins, and of proteins that bind RNA.     

Influence of the chelator structures on the stability of Re and Tc tricarbonyl complexes with iminodiacetic acid tridentate ligands: a computational study

The development of novel radiopharmaceuticals for nuclear medicine based on M(CO)₃ (M?=?Tc, Re) complexes has attracted great attention. The versatility of this core and the easy production of the fac-[M(CO)₃(H₂O)₃]⁺ precursor could explain this interest. The main characteristics of these tricarbonyl complexes are the high substitution stability of the three CO ligands and the corresponding lability of the coordinated water molecules, yielding, via easy exchange of a variety of bi- and tridentate ligands, complexes xof very high kinetic stability. Here, a computational study of different tricarbonyl complexes of Re(I) and Tc(I) was performed using density functional theory. The solvent effect was simulated using the polarizable continuum model. These structures were used as a starting point to investigate the relative stabilities of tricarbonyl complexes with various tridentate ligands. These complexes included an iminodiacetic acid unit for tridentate coordination to the fac-[M(CO)₃]⁺ moiety (M?=?Re, Tc), an aromatic ring system bearing a functional group (?NO₂, ?NH₂, and –Cl) as a linking site model, and a tethering moiety (a methylene, ethylene, propylene butylene, or pentylene bridge) between the linking and coordinating sites. The optimized complexes showed geometries comparable to those inferred from X-ray data. In general, the Re complexes were more stable than the corresponding Tc complexes. Furthermore, using NH₂ as the functional group, a medium length carbon chain, and ortho substitution increased complex stability. All of the bonds involving the metal center presented a closed shell interaction with dative or covalent character, and the strength of these bonds decreased in the sequence Tc-CO?>?Tc-O?>?Tc-N.     

Solution and solid state study of copper(II) ternary complexes containing amino acids of interest for brain biochemistry - 1: Aspartic or glutamic acids with methionine or cysteine

Four new ternary complexes of Cu(II) containing aspartic or glutamic acids and methionine or cysteine as ligands were studied both in solution and in solid state. The solution study was performed using potentiometry, UV-Vis spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and electrochemistry. The stability constants of the ternary complexes were determined by potentiometry. The order of the values for the stability constants was CuGluMet (complex 4) < CuAspMet (complex 2) < CuGluCys (complex 3) < CuAspCys (complex 1), with complex 1 ≈ complex 3 ? complex 2 ≈ complex 4. This behavior was confirmed by the electronic spectra, EPR parameters and cyclic voltammetry. The compounds were synthesized in the solid state and characterized by thermogravimetry as well as vibrational and EPR spectroscopy. The results found in solid state are in agreement with the data found in solution studies where methionine, aspartic and glutamic acids coordinate to the copper(II) ion using the nitrogen atom of the amino group and one oxygen atom of the carboxylate group and cysteine coordinates through the nitrogen and sulfur atoms. The EPR data suggest that the complexes are square planar and that the complexes with cysteine as one of the ligands have some distortion.