Glycosylation of yeast aspartyl-tRNA synthetase. Affinity labelling by glucose and glucose 6-phosphate

Exceptionally versatile – arginine in bacterial post-translational protein modifications

Post-translational modifications (PTM) are the evolutionary solution to challenge and extend the boundaries of genetically predetermined proteomic diversity. As PTMs are highly dynamic, they also hold an enormous regulatory potential. It is therefore not surprising that out of the 20 proteinogenic amino acids, 15 can be post-translationally modified. Even the relatively inert guanidino group of arginine is subject to a multitude of mostly enzyme mediated chemical changes. The resulting alterations can have a major influence on protein function. In this review, we will discuss how bacteria control their cellular processes and develop pathogenicity based on post-translational protein-arginine modifications.

Mapping Post-Transcriptional Modifications onto Transfer Ribonucleic Acid Sequences by Liquid Chromatography Tandem Mass Spectrometry

Liquid chromatography, coupled with tandem mass spectrometry, has become one of the most popular methods for the analysis of post-transcriptionally modified transfer ribonucleic acids (tRNAs). Given that the information collected using this platform is entirely determined by the mass of the analyte, it has proven to be the gold standard for accurately assigning nucleobases to the sequence. For the past few decades many labs have worked to improve the analysis, contiguous to instrumentation manufacturers developing faster and more sensitive instruments. With biological discoveries relating to ribonucleic acid happening more frequently, mass spectrometry has been invaluable in helping to understand what is happening at the molecular level. Here we present a brief overview of the methods that have been developed and refined for the analysis of modified tRNAs by liquid chromatography tandem mass spectrometry.

Genetic control of amadori product degradation in Bacillus subtilis via regulation of frlBONMD expression by FrlR

Bacillus subtilis is capable of degrading fructosamines. The phosphorylation and the cleavage of the resulting fructosamine 6-phosphates is catalyzed by the frlD and frlB gene products, respectively. This study addresses the physiological importance of the frlBONMD genes (formerly yurPONML), revealing the necessity of their expression for growth on fructosamines and focusing on the complex regulation of the corresponding transcription unit. In addition to the known regulation by the global transcriptional regulator CodY, the frl genes are repressed by the convergently transcribed FrlR (formerly YurK). The latter causes repression during growth on substrates other than fructosamines. Additionally, we identified in the first intergenic region of the operon an FrlR binding site which is centrally located within a 38-bp perfect palindromic sequence. There is genetic evidence that this sequence, in combination with FrlR, contributes to the remarkable decrease in the transcription downstream of the first gene of the frl operon.

Histone H1 as a Reporter Protein to Investigate Glycation in Bacteria

Nonenzymatic glycosylation (glycation) of proteins is a multistage chemical process starting as a condensation reaction between reducing sugars and primary amino groups (mainly from the side chains of Lis and Arg) and ending up with formation of complex heterocyclic compounds called advanced glycation end products (AGEs). For a long time, glycation has been attributed to the long-lived eukaryotes (including in humans) only. In a recent study, we showed that glycation also occurs in bacteria. The present study aims to prove that bacterial cytoplasm contains soluble glycating compounds. To this end, Lis/Arg-rich histone H1 isolated from rat liver was treated with deproteinized Escherichia coli cytoplasm through a dialysis membrane. This treatment leads to accumulation of AGEs as well as to a remarkable degradation of the reporter protein on storage at 4 degrees C. Our results indicate also that glycation can be inhibited by acetylsalicylic acid (aspirin), thiamine (vitamin B1), and pyridoxine (vitamin B6).

Evidence for non-enzymatic glycosylation in Escherichia coli

Non-enzymatic glycosylation (glycation) is a chain of chemical reactions affecting free amino groups in proteins of long-living eukaryotes. It proceeds in several steps leading to the consecutive formation of Schiff bases, Amadori products and advanced glycation end-products (AGEs). To our knowledge, this process has not been observed in prokaryotes so far. However, the present study provides clear-cut evidence that glycation takes place in bacteria despite their short life span. We have detected AGEs in recombinant human interferon gamma (rhIFN-gamma) produced in Escherichia coli as well as in total protein of the same bacterium using three different approaches: (i) Western blotting using two monoclonal antibodies raised against AGEs; (ii) fluorescent spectroscopy; and (iii) investigation of the effect of known AGE inhibitors (such as acetyl salicylic acid and thiamine) on the glycation reaction. Our study shows that non-enzymatic glycosylation is initiated during the normal growth of E. coli and results in AGE formation even after isolation of proteins. This process seems to be tightly associated with some post-translational modifications observed in the cysteineless rhIFN-gamma, such as covalent dimerization and truncation.

Evidence for glycation of horse liver alcohol dehydrogenase in vivo

A procedure involving HPLC of N-phenylthiocarbamyl derivatives of N-(1-deoxyhexitolyl) amino acids was used to show that borohydride-treated alcohol dehydrogenase, from horse liver, contained 0.16 mol of N epsilon-(1-deoxyhexitolyl) lysine per mol of enzyme. The identity of this compound was confirmed by mass spectrometry. It was concluded that glycation of alcohol dehydrogenase had occurred in vivo, resulting in the formation of N epsilon-(1-deoxyfructosyl) lysyl residues. The presence of the latter accounted for the retention of 14% of the enzyme by an agaroseboronate gel. These findings are interesting in view of the observation [Tsai, C. S., and White, J. H. (1983) Biochem. J. 209, 309-314] that the enzyme was activated when it was glycated in vitro.

The microheterogeneity of the crystallizable yeast cytoplasmic aspartyl-tRNA synthetase

Yeast aspartyl-tRNA synthetase is a dimeric enzyme (alpha 2, Mr 125,000) which can be crystallized either alone or complexed with tRNAAsp. When analyzed by electrophoretic methods, the pure enzyme presents structural heterogeneities even when recovered from crystals. Up to three enzyme populations could be identified by polyacrylamide gel electrophoresis and more than ten by isoelectric focusing. They have similar molecular masses and mainly differ in their charge. All are fully active. This microheterogeneity is also revealed by ion-exchange chromatography and chromatofocusing. Several levels of heterogeneity have been defined. A first type, which is reversible, is linked to redox effects and/or to conformational states of the protein. A second one, revealed by immunological methods, is generated by partial and differential proteolysis occurring during enzyme purification from yeast cells harvested in growth phase. As demonstrated by end-group analysis, the fragmentation concerns exclusively the N-terminal end of the enzyme. The main cleavage points are Gln-19, Val-20 and Gly-26. Six minor cuts are observed between positions 14 and 33. The present data are discussed in the perspective of the crystallographic studies on aspartyl-tRNA synthetase.

Higher eukaryotic aminoacyl-tRNA synthetases in physiologic and pathologic states

The aminoacyl-tRNA synthetases play a dual role in cell metabolism by synthesizing aminoacyl-tRNAs and an odd dinucleotide diadenosine-5', 5''-P1, P4-tetraphosphate which appears to be involved in DNA replication and the control of cell proliferation. This review is a synthesis of recent results on the structure, genetics, cell biology, physiology, role in neoplasia, and role in autoimmune myositis of the higher eukaryotic aminoacyl-tRNA synthetases.