Méthionine | EPFL Graph Search

La méthionine (abréviations IUPAC-IUBMB : Met et M) est un acide dont l'énantiomère L est l'un des aminés protéinogènes, et l'un des aminés essentiels pour l'Homme. Elle est encodée sur les ARN messagers par le codon AUG. Elle est caractérisée par la présence d'un atome de soufre engagé dans une fonction thioéther. Son groupe méthyle intervient dans de nombreuses réactions de méthylation du métabolisme. Elle joue un rôle critique dans la reproduction, le développement cellulaire, et la méthylation de l'ADN et des protéines. Rôles biologiques La méthionine joue un rôle particulier dans la biosynthèse des protéines, puisque toutes les chaînes protéiques démarrent par l'incorporation d'une méthionine en position N-terminale. D'autres résidus méthionine peuvent ensuite être incorporés de manière interne à la chaîne polypeptidique. La première méthionine des protéines n'est pas toujours retrouvée dans les protéines terminées. Elle est en effet fréquemment clivée par une e

Metal-based chemosensors for amino acids, peptides, and nucleotides

Andrey Buryak

An organometallic 4d transition metal complex [CpRhCl2]2, together with commercially available dyes, was used to construct indicator displacement assays (IDAs) for the detection of peptides, amino acids, and nucleotides. The combination of the CpRh complex with the dye azophloxine was found to form a chemosensing ensemble for the sequence-selective detection of histidine- and methionine-containing peptides in water at neutral pH. A strong interaction of the rhodium complex with peptides bearing histidine or methionine residue in the position 1 or 2 allowed to detect these peptides down to a concentration of 0.3 µM. The same organometallic complex and three commercially available dyes were employed to compose an array of IDA chemosensors for the detection of natural amino acids. We found that the variation of the pH can effectively be used to modulate the selectivity of an IDA sensor. An excellent discrimination of 20 amino acids was achieved. The combination of [Cp*RhCl2]2 with the dyes gallocyanine, evans blue, and mordant yellow 10 forms a multicomponent indicator displacement assay (MIDA), which can be used to sense low millimolar concentrations of nucleotides and the pyrophosphate anion in buffered aqueous solution. Moreover, the MIDA allows to simultaneously determine the concentrations of adenosine triphosphate and pyrophosphate/cyclic adenosine monophosphate with a single UV-Vis measurement. In the second part of our work we investigated whether dynamic combinatorial libraries (DCLs) can be used for sensing purposes. We found that the dyes arsenazo I, methylcalcein blue, and glycine cresol red, in combination with the metal salts CuCl2 and NiCl2, form a DCL of differently colored metal-dye complexes. The addition of an analyte able to interact with a member(s) of such a library, results in a re-equilibraion easily detectable by UV-Vis spectroscopy. Using dipeptides as analytes we demonstrated that this way of sensing is very effective – even closely related peptides such as regio- (Ala-Phe vs. Phe-Ala) and stereo- (Phe-Ala vs. D-Phe-Ala) isomers can easily be discriminated. Additionally, we found that the identity of the best sensor depends on the problem to be addressed.

EPFL2007

Method for Identification of Threonine Isoforms in Peptides by Ultraviolet Photofragmentation of Cold Ions

Vladimir Kopysov, Aleksandr Pereverzev, Elizaveta Solovyeva

Identification of isomeric amino acid residues in peptides and proteins is challenging but often highly desired in proteomics. One of the practically important cases that require isomeric assignments is that associated with single-nucleotide polymorphism substitutions of Met residues by Thr in cancer-related proteins. These genetically encoded substitutions can yet be confused with the chemical modifications, arising from protein alkylation by iodoacetamide, which is commonly used in the standard procedure of sample preparation for proteomic analysis. Similar to the genetically encoded mutations, the alkylation also induces a conversion of methionine residues, but to the iso-threonine form. Recognition of the mutations therefore requires isoform-sensitive detection techniques. Herein, we demonstrate an analytical method for reliable identification of isoforms of threonine residues in tryptic peptides. It is based on ultraviolet photodissociation mass spectrometry of cryogenically cooled ions and a machine-learning algorithm. The measured photodissociation mass spectra exhibit isoform-specific patterns, which are independent of the residues adjacent to threonine or iso-threonine in a peptide sequence. A comprehensive metric-based evaluation demonstrates that, being calibrated with a set of model peptides, the method allows for isomeric identification of threonine residues in peptides of arbitrary sequence.

AMER CHEMICAL SOC2019

Middle-down analysis of monoclonal antibodies with electron transfer dissociation Orbitrap FTMS

Daniel Ayoub, Luca Fornelli, Yury Tsybin

The rapid growth of approved biotherapeutics, e.g., monoclonal antibodies or immunoglobulins G (IgGs), demands improved techniques for their quality control. Traditionally, proteolysis-based bottom-up mass spectrometry (MS) has been employed. However, the long, multistep sample preparation protocols required for bottom-up MS are known to potentially introduce artifacts in the original sample. For this reason, a top-down MS approach would be preferable. The current performance of top-down MS of intact monoclonal Ig Gs, though, enables reaching only up to similar to 30% sequence coverage, with incomplete sequencing of the complementarity determining regions which are fundamental for IgG's antigen binding. Here, we describe a middle-down MS protocol based on the use of immunoglobulin G-degrading enzyme of Streptococcus pyogenes (IdeS), which is capable of digesting IgGs in only 30 min. After chemical reduction, the obtained similar to 25 kDa proteolytic fragments were analyzed by reversed phase liquid chromatography (LC) coupled online with an electron transfer dissociation (ETD)-enabled hybrid Orbitrap Fourier transform mass spectrometer (Orbitrap Elite FTMS). Upon optimization of ETD and product ion transfer parameters, results show that up to similar to 50% sequence coverage for selected IgG fragments is reached in a single LC run and up to similar to 70% when data obtained by distinct LC MS runs are averaged. Importantly, we demonstrate the potential of this middle-down approach in the identification of oxidized methionine residues. The described approach shows a particular potential for the analysis of IgG mixtures.

Amer Chemical Soc2014

Metal-based chemosensors for amino acids, peptides, and nucleotides

Andrey Buryak

EPFL2007