A streamlined workflow for twoplexing of N-linked glycan analysis using light (12C6) and heavy (13C6) isotopologues of 3-aminobenzenesulfonic acid.

Comparative glycosylation analysis of biopharmaceuticals requires the development of methods that deliver the necessary throughput, support structural elucidation and relative quantitation of glycans released from therapeutics. The current study presents the development and applicability assessment of a twoplex approach using light and heavy isotopolouges of 3-aminobenzenesulfonic acid (3-ASA) under wet labeling conditions followed by UHPLC-MS analysis in data dependent acquisition mode. Excellent labelling efficiency, >90%, was achieved for both the light and heavy variants of the reagent. Glycan distributions of two human IgG lots labeled by light and heavy isotopolouges were identical, demonstrating no labeling bias introduced by either of the isotopologues. Peak area distributions of glycan profiles of two human IgG lots were compared to 2-aminobenzamide (2-AB) and RapiFluor-MS protocols. The comparison led to identical results in peak area distribution across the three dyes, but differences in chromatographic selectivity attributed to the different tags. MS1 based relative quantitation was further validated by releasing glycans from the same lot of human IgG, with glycan pools obtained labeled with light and heavy isotopologues separately, followed by mixing and clean-up of the same amount of light and heavy labeled glycan pools. MS analyses of each glycan resulted in a ratio of light and heavy XIC in the range of 0.97 ≤ x ≤ 1.05, demonstrating the method is amenable for the relative quantitation of glycans. Excellent correlation between the relative quantitation data of N-glycans from two human IgG N-glycan pools using the twoplex approach and ratios from peak area distribution calculated from the fluorescent chromatogram was observed (r = 0.986), further corroborating the reliability of the method and its potential applicability in the biopharmaceutical industry. Highly informative HCD-MS2 spectra dominated mostly by Y- and Z-type single and double glycosidic fragment ions facilitate structural interpretation of the oligosaccharides.

Separation of Sialylated Glycan Isomers by Differential Mobility Spectrometry.

Mass spectrometry has proven itself to be an important technology for characterizing intact glycoproteins, glycopeptides, and released glycans. However, these molecules often present significant challenges during analysis. For example, glycans of identical molecular weights can be present in many isomeric forms, with one form having dramatically more biological activity than the others. Discriminating among these isomeric forms using mass spectrometry alone can be daunting, which is why orthogonal techniques, such as ion mobility spectrometry, have been explored. Here, we demonstrate the use of differential mobility spectrometry (DMS) to separate isomeric glycans differing only in the linkages of sialic acid groups (e.g., α 2,3 versus α 2,6). This ability extends from a small trisaccharide species to larger biantennary systems and is driven, in part, by the role of intramolecular solvation of the charge site(s) on these ions within the DMS environment.

Biochemical comparison of Anopheles gambiae and human NADPH P450 reductases reveals different 2'-5'-ADP and FMN binding traits.

NADPH-cytochrome P450 oxidoreductase (CPR) plays a central role in chemical detoxification and insecticide resistance in Anopheles gambiae, the major vector for malaria. Anopheles gambiae CPR (AgCPR) was initially expressed in Eschericia coli but failed to bind 2',5'-ADP Sepharose. To investigate this unusual trait, we expressed and purified a truncated histidine-tagged version for side-by-side comparisons with human CPR. Close functional similarities were found with respect to the steady state kinetics of cytochrome c reduction, with rates (k(cat)) of 105 s(-1) and 88 s(-1), respectively, for mosquito and human CPR. However, the inhibitory effects of 2',5'-ADP on activity were different; the IC(50) value of AgCPR for 2',5'-ADP was significantly higher (6-10 fold) than human CPR (hCPR) in both phosphate and phosphate-free buffer, indicative of a decrease in affinity for 2',5'-ADP. This was confirmed by isothermal titration calorimetry where binding of 2',5'-ADP to AgCPR (K(d) = 410±18 nM) was ∼10 fold weaker than human CPR (K(d) = 38 nM). Characterisation of the individual AgFMN binding domain revealed much weaker binding of FMN (K(d) = 83±2.0 nM) than the equivalent human domain (K(d) = 23±0.9 nM). Furthermore, AgCPR was an order of magnitude more sensitive than hCPR to the reductase inhibitor diphenyliodonium chloride (IC(50) = 28 µM±2 and 361±31 µM respectively). Taken together, these results reveal unusual biochemical differences between mosquito CPR and the human form in the binding of small molecules that may aid the development of 'smart' insecticides and synergists that selectively target mosquito CPR.