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Publications - Cell and Metabolic Biology

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Publications

Frolov, A.; Hoffmann, R.; Identification and relative quantification of specific glycation sites in human serum albumin Anal. Bioanal. Chem. 397, 2349-2356, (2010) DOI: 10.1007/s00216-010-3810-9

Glycation (or non-enzymatic glycosylation) is a common non-enzymatic covalent modification of human proteins. Glucose, the highest concentrated monosaccharide in blood, can reversibly react with amino groups of proteins to form Schiff bases that can rearrange to form relatively stable Amadori products. These can be further oxidized to advanced glycation end products (AGEs). Here, we analyzed the glycation patterns of human serum albumin (HSA) in plasma samples obtained from five patients with type 2 diabetes mellitus. Therefore, glycated peptides from a tryptic digest of plasma were enriched with m-aminophenylboronic acid (mAPBA) affinity chromatography. The glycated peptides were then further separated in the second dimension by RP-HPLC coupled on-line to an electrospray ionization (ESI) tandem mass spectrometer (MS/MS). Altogether, 18 Amadori peptides, encompassing 40% of the HSA sequence, were identified. The majority of the peptides were detected and relatively quantified in all five samples with a high reproducibility among the replicas. Eleven Lys-residues were glycated at similar quantities in all samples, with glycation site Lys549 (KAm(Glc)QTALVELVK) being the most abundant. In conclusion, the established mAPBA/nanoRP-HPLC-ESI-MS/MS approach could reproducibly identify and quantify glycation sites in plasma samples, potentially useful in diagnosis and therapeutic control.
Publications

Fedorova, M.; Frolov, A.; Hoffmann, R.; Fragmentation behavior of Amadori-peptides obtained by non-enzymatic glycosylation of lysine residues with ADP-ribose in tandem mass spectrometry J. Mass Spectrom. 45, 664-669, (2010) DOI: 10.1002/jms.1758

Mono‐ and poly‐adenosine diphosphate (ADP)‐ribosylation are common post‐translational modifications incorporated by sequence‐specific enzymes at, predominantly, arginine, asparagine, glutamic acid or aspartic acid residues, whereas non‐enzymatic ADP‐ribosylation (glycation) modifies lysine and cysteine residues. These glycated proteins and peptides (Amadori‐compounds) are commonly found in organisms, but have so far not been investigated to any great degree. In this study, we have analyzed their fragmentation characteristics using different mass spectrometry (MS) techniques. In matrix‐assisted laser desorption/ionization (MALDI)‐MS, the ADP‐ribosyl group was cleaved, almost completely, at the pyrophosphate bond by in‐source decay. In contrast, this cleavage was very weak in electrospray ionization (ESI)‐MS. The same fragmentation site also dominated the MALDI‐PSD (post‐source decay) and ESI‐CID (collision‐induced dissociation) mass spectra. The remaining phospho‐ribosyl group (formed by the loss of adenosine monophosphate) was stable, providing a direct and reliable identification of the modification site via the b‐ and y‐ion series. Cleavage of the ADP‐ribose pyrophosphate bond under CID conditions gives access to both neutral loss (347.10 u) and precursor‐ion scans (m/z 348.08), and thereby permits the identification of ADP‐ribosylated peptides in complex mixtures with high sensitivity and specificity. With electron transfer dissociation (ETD), the ADP‐ribosyl group was stable, providing ADP‐ribosylated c‐ and z‐ions, and thus allowing reliable sequence analyses.
Publications

Ehrlich, H.; Hanke, T.; Simon, P.; Born, R.; Fischer, C.; Frolov, A.; Langrock, T.; Hoffmann, R.; Schwarzenbolz, U.; Henle, T.; Bazhenov, V. V.; Worch, H.; Carboxymethylation of the fibrillar collagen with respect to formation of hydroxyapatite J. Biomed. Mater. Res. B 92B, 542-551, (2010) DOI: 10.1002/jbm.b.31551

Control over crystal growth by acidic matrix macromolecules is an important process in the formation of many mineralized tissues. Highly acidic macromolecules are postulated intermediates in tissue mineralization, because they sequester many calcium ions and occur in high concentrations at mineralizing foci in distantly related organisms. A prerequisite for biomineralization is the ability of cations like calcium to bind to proteins and to result in concert with appropriate anions like phosphates or carbonates in composite materials with bone‐like properties. For this mineralization process the proteins have to be modified with respect to acidification. In this study we modified the protein collagen by carboxymethylation using glucuronic acid. Our experiments showed unambigously, that Nε‐carboxymethyllysine is the major product of the in vitro nonenzymatic glycation reaction between glucuronic acid and collagen. We hypothesized that the function of biomimetically carboxymethylated collagen is to increase the local concentration of corresponding ions so that a critical nucleus of ions can be formed, leading to the formation of the mineral. Thus, the self‐organization of HAP nanocrystals on and within collagen fibrils was intensified by carboxymethylation.
Publications

Ehrlich, H.; Hanke, T.; Frolov, A.; Langrock, T.; Hoffmann, R.; Fischer, C.; Schwarzenbolz, U.; Henle, T.; Born, R.; Worch, H.; Modification of collagen in vitro with respect to formation of Nɛ-carboxymethyllysine Int. J. Biol. Macromol. 44, 51-56, (2009) DOI: 10.1016/j.ijbiomac.2008.10.001

Developing new biopolymer-based materials with bio-identical properties is a significant challenge in modern science. One interesting route to this goal involves the biomineralization of collagen, a pre-structured and widely available protein, into a material with interesting properties. A prerequisite for biomineralization is the ability of cations (e.g., calcium) to bind to the protein and to result in concert with appropriate anions (e.g., phosphate) in composite material with e.g., bone-like properties. In order to increase the number of binding sites it is necessary to modify the protein prior to mineralization. For this glucuronic acid (GA) was used due to its carbonyl and carboxyl groups to derivatize proteinogenic amino groups transferring them into negatively charged carboxyl groups. Our experiments showed for the first time, that Nɛ-carboxymethyllysine is the major product of in vitro non-enzymatic glycosylation of collagen by glucuronic acid. For an unequivocal determination of the reaction products, the lysine residues of collagen and of the model peptide were carboxymethylated through a reductive alkylation with glyoxalic acid and compared to the glucuronic acid derivatives. Beside their identical mass spectra the common structure elements could be confirmed with FTIR. Thus, in the context of matrix engineering, by producing Nɛ-carboxymethyllysine, glucuronic acid offers a convenient way of introducing additional stable acidic groups into protein matrices.
Publications

Ehrlich, H.; Hanke, T.; Born, R.; Fischer, C.; Frolov, A.; Langrock, T.; Hoffmann, R.; Schwarzenbolz, U.; Henle, T.; Simon, P.; Geiger, D.; Bazhenov, V. V.; Worch, H.; Mineralization of biomimetically carboxymethylated collagen fibrils in a model dual membrane diffusion system J. Membr. Sci. 326, 254-259, (2009) DOI: 10.1016/j.memsci.2008.10.003

In the present work, we show for the first time, that Nɛ-carboxymethyllysine is the major product of the in vitro non-enzymatic glycation reaction between fibrillar collagen and glucuronic acid. Dual diffusion membrane system was effectively used for oriented crystal growth of octacalcium phosphate/hydroxyapatite on the biomimetically carboxymethylated collagen fibrils. We hypothesize that the function of biomimetically carboxymethylated collagen is to increase the local concentration of corresponding ions in such a way that a critical nucleus of ions can be formed, leading to the formation of the mineral under specific micro-environment conditions achieved by using diffusion membrane system.
Books and chapters

Frolov, A.; Singer, D.; Zauner, T.; Hoffmann, R.; Solid Phase Synthesis and Analysis of Amadori Peptides Adv. Exp. Med. Biol. 611, 423-424, (2009) ISBN: 978-0-387-73657-0 DOI: 10.1007/978-0-387-73657-0_182

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