Characterization of immunoglobulins through analysis of N-glycopeptides by MALDI-TOF MS.

The aim of this report is to emphasize the role, usefulness and power of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) in the analysis of glycoforms of antibodies (Abs) through their proteolytic glycopeptides. Abs are complex biomolecules in which glycans hold determinant properties and thus need to be thoroughly characterized following Ab production by recombinant methods or Ab collection from human/animal serum or tissue. In spite of the great robustness of MALDI-TOF MS in terms of tolerance to impurities, the analysis of Abs and Ab components using this technique requires extensive sample preparation involving all or some of chromatography, solid phase extraction, enzymatic modification, and chemical derivatization. This report focuses on a monoclonal Ab produced in cell culture, as well as on a polyclonal human immunoglobulin (Ig) G obtained commercially and a polyclonal porcine IgG obtained from serum. A method is first provided to separate Ab protein chain components (light chains, heavy chains) by gel electrophoresis, which is useful for instance for protein-A eluates of Igs either from cell culture or biological samples. This allows for in-gel proteolytic digestion of the protein gel band(s) of choice for further MS characterization. Also discussed is the more conventional in-solution overnight digestion method used here with each of two proteolytic enzymes, i.e. trypsin and chymotrypsin. The overnight method is in turn compared with a much faster approach, that of digesting Abs with trypsin or chymotrypsin through the action of microwave heating. For method comparison, glycopeptides are fractionated from digestion mixtures using mostly C-18 cartridges for simplicity, although this enrichment procedure is also compared with other published procedures. The advantages of MALDI tandem mass spectrometry are highlighted for glycopeptide analysis, and lastly an esterification method applied to glycopeptides is discussed for retention of sialic acid residues on peptide acidic glycoforms.

Rapid screening of Alternaria mycotoxins using MALDI-TOF mass spectrometry.

BACKGROUND: Members of the Alternaria genus produce various toxins whose occurrence in agricultural commodities is a major concern for humans and the environment. The present study developed a simple and efficient matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) method for the rapid detection of Alternaria toxins. RESULTS: A new method for the detection of alternariol (AOH), alternariol monomethyl ether (AME) and tentoxin (TEN) by MALDI-TOF MS was developed. Different solid phase extraction (SPE) clean-up methods were tried to optimize the purification of wheat matrix, and an optimal extraction method was designed to recover the three Alternaria toxins. In addition, various MALDI matrices were examined and α-cyano-4-hydroxycinnamic acid (CHCA) matrix gave good repeatability for all three Alternaria toxins. CONCLUSION: This is the first study to report the detection of three important Alternaria toxins concurrently using MALDI-TOF MS and opens up the possibility of rapid screening of Alternaria toxins in several other cereals and food products. © 2016 Her Majesty the Queen in Right of Canada Journal of the Science of Food and Agriculture © 2016 Society of Chemical Industry.

Algal carbohydrates affect polyketide synthesis of the lichen-forming fungus Cladonia rangiferina.

Lichen secondary metabolites (polyketides) are produced by the fungal partner, but the role of algal carbohydrates in polyketide biosynthesis is not clear. This study examined whether the type and concentration of algal carbohydrate explained differences in polyketide production and gene transcription by a lichen fungus (Cladonia rangiferina). The carbohydrates identified from a free-living cyanobacterium (Spirulina platensis; glucose), a lichen-forming alga (Diplosphaera chodatii; sorbitol) and the lichen alga that associates with C. rangiferina (Asterochloris sp.; ribitol) were used in each of 1%, 5% and 10% concentrations to enrich malt yeast extract media for culturing the mycobiont. Polyketides were determined by high performance liquid chromatography (HPLC), and polyketide synthase (PKS) gene transcription was measured by quantitative PCR of the ketosynthase domain of four PKS genes. The lower concentrations of carbohydrates induced the PKS gene expression where ribitol up-regulated CrPKS1 and CrPKS16 gene transcription and sorbitol up-regulated CrPKS3 and CrPKS7 gene transcription. The HPLC results revealed that lower concentrations of carbon sources increased polyketide production for three carbohydrates. One polyketide from the natural lichen thallus (fumarprotocetraric acid) also was produced by the fungal culture in ribitol supplemented media only. This study provides a better understanding of the role of the type and concentration of the carbon source in fungal polyketide biosynthesis in the lichen Cladonia rangiferina.

Mass spectrometric analysis of core fucosylation and sequence variation in a human-camelid monoclonal antibody.

Electrospray mass spectrometry (ESI-MS) was used to measure the masses of an intact dimeric monoclonal antibody (Mab) and assess the fucosylation level. The Mab under study was EG2-hFc, a chimeric human-camelid antibody of about 80 kDa (A. Bell et al., Cancer Lett., 2010, 289(1), 81-90). It was obtained from cell culture with and without a fucosylation inhibitor, and treated with EndoS which cleaves between the two core N-acetyl glucosamine (GlcNAc) residues. It is the first time that this combined approach with a unique mass spectrometer was used to measure 146 Da differences as part of a large intact dimeric antibody. Results showed that in the dimer, both heavy chains were fucosylated on the core GlcNAc of the Fc Asn site equivalent to Asn297. In the presence of the fucosylation inhibitor, fucosylation was lost on both subunits. Following reduction, monomers were analyzed and the masses obtained corroborated the dimer results. Dimeric EG2-hFc Mab treated with PNGase F, to deglycosylate the protein, was also measured by MS for mass comparison. In spite of the success of fucosylation level measurements, the experimental masses of deglycosylated dimers and GlcNAc-Fuc bearing dimers did not correspond to masses of our sequence of reference (A. Bell et al., Cancer Lett., 2010, 289(1), 81-90; ; ), which prompted experiments to determine the protein backbone sequence. Digest mixtures from trypsin, GluC, as well as trypsin + GluC proteolysis were analyzed by matrix-assisted laser desorption/ionization (MALDI) MS and MS/MS. A few variations were found relative to the reference sequence, which are discussed in detail herein. These measurements allowed us to build a new "experimental" sequence for the EG2-hFc samples investigated in this work, although there are still ambiguities to be resolved in this new sequence. MALDI-MS/MS also confirmed the fucosylation pattern in the Fc tryptic peptide EEQYNSTYR.

Absolute Quantitation of Glycoforms of Two Human IgG Subclasses Using Synthetic Fc Peptides and Glycopeptides.

Immunoglobulins, such as immunoglobulin G (IgG), are of prime importance in the immune system. Polyclonal human IgG comprises four subclasses, of which IgG1 and IgG2 are the most abundant in healthy individuals. In an effort to develop an absolute MALDI-ToF-MS quantitative method for these subclasses and their Fc N-glycoforms, (glyco)peptides were synthesized using a solid-phase approach and used as internal standards. Tryptic digest glycopeptides from monoclonal IgG1 and IgG2 samples were first quantified using EEQYN(GlcNAc)STYR and EEQFN(GlcNAc)STFR standards, respectively. For IgG1, a similar glycopeptide where tyrosine (Y) was isotopically labelled was used to quantify monoclonal IgG1 that had been treated with the enzyme Endo-F2, i.e., yielding tryptic glycopeptide EEQYN(GlcNAc)STYR. The next step was to quantify single subclasses within polyclonal human IgG samples. Although ion abundances in the MALDI spectra often showed higher signals for IgG2 than IgG1, depending on the spotting solvent used, determination of amounts using the newly developed quantitative method allowed to obtain accurate concentrations where IgG1 species were predominant. It was observed that simultaneous analysis of IgG1 and IgG2 yielded non-quantitative results and that more success was obtained when subclasses were quantified one by one. More experiments served to assess the respective extraction and ionization efficiencies of EEQYNSTYR/EEQFNSTFR and EEQYN(GlcNAc)STYR/EEQFN(GlcNAc)STFR mixtures under different solvent and concentration conditions. Graphical Abstract ᅟ.

A validated fast difference spectrophotometric method for 5-hydroxymethyl-2-furfural (HMF) determination in corn syrups.

Corn syrups, important ingredients used in food and beverage industries, often contain high levels of 5-hydroxymethyl-2-furfural (HMF), a toxic contaminant. In this work, an in house validation of a difference spectrophotometric method for HMF analysis in corn syrups was developed using sophisticated statistical tools by the first time. The methodology showed excellent analytical performance with good selectivity, linearity (R2=99.9%, r>0.99), accuracy and low limits (LOD=0.10mgL-1 and LOQ=0.34mgL-1). An excellent precision was confirmed by repeatability (RSD (%)=0.30) and intermediate precision (RSD (%)=0.36) estimates and by Horrat value (0.07). A detailed study of method precision using a nested design demonstrated that variation sources such as instruments, operators and time did not interfere in the variability of results within laboratory and consequently in its intermediate precision. The developed method is environmentally friendly, fast, cheap and easy to implement resulting in an attractive alternative for corn syrups quality control in industries and official laboratories.

Rapid Screening of Ergot Alkaloids in Sclerotia by MALDI-TOF Mass Spectrometry.

Ergot is a common disease of wheat and other cereal grains that is predominantly caused by Claviceps purpurea in the field, often affecting crop yield in addition to the environment. Infected grain can be contaminated with dark sclerotia, which contain fungal metabolites such as ergot alkaloids. The occurrence of ergot alkaloids in cereal grain is a major health concern for humans and livestock. Effective and rapid screening of these mycotoxins is crucial for producers, processors, and consumers of cereal-based food and feed grain. Established methods of ergot alkaloid screening based on LC-MS or GC-MS require laborious processes. A novel method using matrix-assisted laser desorption ionization (MALDI)-time-of-flight (TOF) MS was developed to identify four ergot alkaloids. Using dihydroxybenzoic acid as the matrix, ergosine, ergocornine, ergocryptine, and ergocristine were readily detected in individual sclerotia of C. purpurea. The accuracy of the identified ergot alkaloids was further confirmed by tandem MS analysis. MALDI-TOF MS is suitable for high-throughput screening of ergot alkaloids because it permits rapid and accurate identification, simple sample preparation, and no derivatization or chromatographic separation.

In house validation from direct determination of 5-hydroxymethyl-2-furfural (HMF) in Brazilian corn and cane syrups samples by HPLC-UV.

In this work the development and in house validation of the HMF direct determination in corn and cane syrups by HPLC-UV was carried out for the first time. The separation was done with isocratic elution of a mobile phase comprising water (with 0.5% formic acid) and acetonitrile (90:10, v/v) on Phenomenex C18 column (5.0 µm, 4.6 × 150 mm), at 30 °C, flow rate of 0.8 mL min(-1) and detection at 285 nm. The validated method showed excellent performance with low limits (LOD and LOQ of 0.09 and 0.26 mg L(-1), respectively), good accuracy (recovery rates between 100% and 104%) and precision (RSD's for repeatability and intermediate precision between 0.57% and 6.43%). Good selectivity and linearity were also observed. HMF contents in both foods were very high (406.6-2121.3 mg kg(-1) for corn syrup and 109.2-893.1 mg kg(-1) for cane syrup), which arouses concern about food safety of these products.