Use of a stable-isotope-labeled reporter peptide and antioxidants for reliable quantification of methionine oxidation in a monoclonal antibody by liquid chromatography/mass spectrometry.

RATIONALE: Accurate quantification of methionine oxidation in therapeutic proteins by liquid chromatography/mass spectrometry (LC/MS) is challenging due to the potential artifacts introduced during sample preparation and analysis in the peptide mapping workflow. In this study, a systematic approach for optimization of the peptide mapping procedure to achieve reliable quantification of endogenous methionine oxidation in monoclonal antibodies was developed. METHODS: The approach is based on usage of a stable-isotope-labeled reporter peptide, identical in sequence to the tryptic peptide of an IgG1 monoclonal antibody containing the methionine residue most prone to oxidation. This approach was applied to evaluating various desalting procedures, and tested on nanoLC/MS, microLC/MS and UPLC/MS for the peptide mapping analysis of a model monoclonal antibody IgG1 sensitive to oxidation. RESULTS: Several steps in the peptide mapping procedure with LC/MS detection at which protein oxidation occurred were identified and optimized using the reference stable-isotope-labeled peptide. Thus, reliable quantification of methionine oxidation in the target monoclonal antibody was validated. CONCLUSIONS: The methodology which utilizes the reference stable-isotope-labeled reporter peptide is applicable to monoclonal antibody oxidation analysis and could be extended to other biotherapeutics once oxidation-prone methionine(s) in the protein sequence are identified. Copyright © 2016 John Wiley & Sons, Ltd.

Quantitative proteomic analysis reveals that antioxidation mechanisms contribute to cold tolerance in plantain (Musa paradisiaca L.; ABB Group) seedlings.

Banana and its close relative, plantain are globally important crops and there is considerable interest in optimizing their cultivation. Plantain has superior cold tolerance compared with banana and a thorough understanding of the molecular mechanisms and responses of plantain to cold stress has great potential value for developing cold tolerant banana cultivars. In this study, we used iTRAQ-based comparative proteomic analysis to investigate the temporal responses of plantain to cold stress. Plantain seedlings were exposed for 0, 6, and 24 h of cold stress at 8 °C and subsequently allowed to recover for 24 h at 28 °C. A total of 3477 plantain proteins were identified, of which 809 showed differential expression from the three treatments. The majority of differentially expressed proteins were predicted to be involved in oxidation-reduction, including oxylipin biosynthesis, whereas others were associated with photosynthesis, photorespiration, and several primary metabolic processes, such as carbohydrate metabolic process and fatty acid beta-oxidation. Western blot analysis and enzyme activity assays were performed on seven differentially expressed, cold-response candidate plantain proteins to validate the proteomics data. Similar analyses of the seven candidate proteins were performed in cold-sensitive banana to examine possible functional conservation, and to compare the results to equivalent responses between the two species. Consistent results were achieved by Western blot and enzyme activity assays, demonstrating that the quantitative proteomics data collected in this study are reliable. Our results suggest that an increase of antioxidant capacity through adapted ROS scavenging capability, reduced production of ROS, and decreased lipid peroxidation contribute to molecular mechanisms for the increased cold tolerance in plantain. To the best of our knowledge, this is the first report of a global investigation on molecular responses of plantain to cold stress by proteomic analysis.

Comparative characterization of the glycosylation profiles of an influenza hemagglutinin produced in plant and insect hosts.

The main objective of this study was to characterize the N-linked glycosylation profiles of recombinant hemagglutinin (HA) proteins expressed in either insect or plant hosts, and to develop a mass spectrometry based workflow that can be used in quality control to assess batch-to-batch reproducibility for recombinant HA glycosylation. HA is a surface glycoprotein of the influenza virus that plays a key role in viral infectivity and pathogenesis. Characterization of the glycans for plant recombinant HA from the viral strain A/California/04/09 (H1N1) has not yet been reported. In this study, N-linked glycosylation patterns of the recombinant HAs from both insect and plant hosts were characterized by precursor ion scan-driven data-dependent analysis followed by high-resolution MS/MS analysis of the deglycosylated tryptic peptides. Five glycosylation sites (N11, N23, N276, N287, and N481) were identified containing high mannose type glycans in plant-expressed HAs, and complex type glycoforms for the insect-expressed HA. More than 95% site occupancy was observed for all glycosylation sites except N11, which was 60% occupied. Multiple-reaction monitoring based quantitation analysis was developed for each glycopeptide isoform and the quantitative results indicate that the Man(8) GlcNAc(2) is the dominant glycan for all sites in plant-expressed HAs. The relative abundance of the glycoforms at each specific glycosylation site and the relative quantitation for each glycoform among three HAs were determined. Few differences in the glycosylation profiles were detected between the two batches of plant HAs studied, but there were significant differences between the glycosylation patterns in the HAs generated in plant and insect expression hosts.