Ovalbumin with Glycated Carboxyl Groups Shows Membrane-Damaging Activity

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Most of the applications are presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

Carboxyl Group-Modified Myoglobin Induces TNF-α-Mediated Apoptosis in Leukemia Cells

Previous studies have shown that chemical modification may increase the activity of proteins or confer novel activity to proteins. Some studies have indicated that myoglobin (Mb) is cytotoxic; however, the underlying mechanisms remain unclear. In this study, we investigated whether chemical modification of the carboxyl group by semicarbazide could promote the Mb cytotoxicity in human leukemia U937 cells and the underlying mechanism of semicarbazide-modified myoglobin (SEM-Mb)-induced U937 cell death. The semicarbazide-modified Mb (SEM-Mb) induced U937 cell apoptosis via the production of cleaved caspase-8 and t-Bid, while silencing of FADD abolished this effect. These findings suggest that SEM-Mb can induce U937 cell death by activating the death receptor-mediated pathway. The SEM-Mb inhibited miR-99a expression, leading to increased NOX4 mRNA and protein expression, which promoted SIRT3 degradation, and, in turn, induced ROS-mediated p38 MAPK phosphorylation. Activated p38 MAPK stimulated miR-29a-dependent tristetraprolin (TTP) mRNA decay. Downregulation of TTP slowed TNF-α mRNA turnover, thereby increasing TNF-α protein expression. The SEM-Mb-induced decrease in cell viability and TNF-α upregulation were alleviated by abrogating the NOX4/SIRT3/ROS/p38 MAPK axis or ectopic expression of TTP. Taken together, our results demonstrated that the NOX4/SIRT3/p38 MAPK/TTP axis induces TNF-α-mediated apoptosis in U937 cells following SEM-Mb treatment. A pathway regulating p38 MAPK-mediated TNF-α expression also explains the cytotoxicity of SEM-Mb in the human leukemia cell lines HL-60, THP-1, K562, Jurkat, and ABT-199-resistant U937. Furthermore, these findings suggest that the carboxyl group-modified Mb is a potential structural template for the generation of tumoricidal proteins.

DMTMM-Mediated Intramolecular Cyclization of Acidic Residues in Peptides/Proteins

The formation of succinimide in proteins has attracted considerable attention in protein aging and biopharmaceutical research. The succinimide formation occurs spontaneously in proteins and is prone to hydrolysis to yield aspartate and isoaspartate, resulting in altered protein functions. Herein, we demonstrated that the coupling reagent 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM) can mediate intramolecular cyclization of aspartic acid to form succinimide efficiently in the LL37-derived short antimicrobial peptide KR12. The formation of succinimide in KR12 was confirmed by liquid chromatography tandem mass spectrometry and nuclear magnetic resonance. Moreover, the succinimide-containing KR12 displayed decreased antimicrobial activity, helicity, and serum stability in comparison with unmodified KR12. The succinimide formation usually changes the protein structure and function, and only in rare cases, it can help to maintain the protein stability. In addition to succinimide, DMTMM can also mediate intraresidue cyclization of N-terminal glutamate to form pyroglutamate. Our work thus provides a convenient and efficient method for preparation of succinimide/pyroglutamate-containing peptides, which can be used for studying their impact on peptide/protein function.

Blocking of negative charged carboxyl groups converts Naja atra neurotoxin to cardiotoxin-like protein

Naja atra cobrotoxin and cardiotoxin 3 (CTX3) exhibit neurotoxicity and cytotoxicity, respectively. In the present study, we aimed to investigate whether the carboxyl groups of cobrotoxin play a role in structural constraints, thereby preventing cobrotoxin from exhibiting cytotoxic activity. Six of the seven carboxyl groups in cobrotoxin were conjugated with semicarbazide. Measurement of circular dichroism spectra and Trp fluorescence quenching showed that the gross conformation of semicarbazide-modified cobrotoxin (SEM-cobrotoxin) and cobrotoxin differed. In sharp contrast to cobrotoxin, SEM-cobrotoxin demonstrated membrane-damaging activity and cytotoxicity, which are feature more characteristic of CTX3. Furthermore, both SEM-cobrotoxin and CTX3 induced cell death through AMPK activation. Analyses of the interaction between polydiacetylene/lipid vesicles and fluorescence-labeled lipids revealed that SEM-cobrotoxin and cobrotoxin adopted different membrane-bound states. The structural characteristics of SEM-cobrotoxin were similar to those of CTX3, including trifluoroethanol (TFE)-induced structural transformation and membrane binding-induced conformational change. Conversely, cobrotoxin was insensitive to the TFE-induced effect. Collectively, the data of this study indicate that blocking negatively charged residues confers cobrotoxin with membrane-damaging activity and cytotoxicity. The findings also suggest that the structural constraints imposed by carboxyl groups control the functional properties of snake venom α-neurotoxins during the divergent evolution of snake venom neurotoxins and cardiotoxins.