Analysis of methylated amino acids by high-performance liquid chromatography: methylation of myelin basic protein

A liquid chromatography tandem mass spectroscopy approach for quantification of protein methylation stoichiometry

Post-translational modifications are biologically important and wide-spread modulators of protein function. Although methods for detecting the presence of specific modifications are becoming established, approaches for quantifying their mol modification/mol protein stoichiometry are less well developed. Here we introduce a ratiometric, label-free, targeted liquid chromatography tandem mass spectroscopy-based method for estimating Lys and Arg methylation stoichiometry on post-translationally modified proteins. Methylated Lys and Arg were detected with limits of quantification at low fmol and with linearity extending from 20 to 5000 fmol. This level of sensitivity allowed estimation of methylation stoichiometry from microgram quantities of various proteins, including those derived from either recombinant or tissue sources. The method also disaggregated total methylation stoichiometry into its elementary mono-, di-, and tri-methylated residue components. In addition to being compatible with kinetic experiments of protein methylation, the approach will be especially useful for characterizing methylation states of proteins isolated from cells and tissues.

RNA and protein interactions modulated by protein arginine methylation

This review summarizes the current status of protein arginine N-methylation reactions. These covalent modifications of proteins are now recognized in a number of eukaryotic proteins and their functional significance is beginning to be understood. Genes that encode those methyltransferases specific for catalyzing the formation of asymmetric dimethylarginine have been identified. The enzyme modifies a number of generally nuclear or nucleolar proteins that interact with nucleic acids, particularly RNA. Postulated roles for these reactions include signal transduction, nuclear transport, or a direct modulation of nucleic acid interactions. A second methyltransferase activity that symmetrically dimethylates an arginine residue in myelin basic protein, a major component of the axon sheath, has also been characterized. However, a gene encoding this activity has not been identified to date and the cellular function for this methylation reaction has not been clearly established. From the analysis of the sequences surrounding known arginine methylation sites, we have determined consensus methyl-accepting sequences that may be useful in identifying novel substrates for these enzymes and may shed further light on their physiological role.

Post-translational chemical modifications of proteins--III. Current developments in analytical procedures of identification and quantitation of post-translational chemically modified amino acid(s) and its derivatives

1. The Chemical modifications of amino acids and their derivatives are mainly due to different post-translational enzymatic reactions. 2. The enzymatic reactions resulting in amino acids such as acetylation-, formylation, methylation-phosphorylation-, sulfation-, hydroxylation, ADP ribosylation-, carboxylation-, amidation-, adenylylation-, glycosylation-, ubiquitination-, prenylation and acylation are listed and analytical methods are reported and extensively reviewed. 3. The post-translationally modified cross-linking molecules after maturations such as desmosines, allo-desmosine, hydroxy-, lysylpyridinoline, 3-hydroxypyridinium derivatives, cyclopentenosine recently found in matured elastin, and in collagen, and pulcherosine a novel tyrosine-derived found in fertilization envelope of Sea Urchin embryo, di-tyrosine in resilin, gamma-glutamyl-lysine isopeptide cross-linking molecule etc. are listed and both physico-chemical and analytical methods are extensively reviewed and discussed. 4. Other consequences of post-translational modifications encountered in the analytical procedure such as N-terminal step-wise Edman degradation of glycosylated site(s), phosphorylated-site(s) and or sulfated-site(s) were also reported by us.