Quality Control and Automation Friendly GlycoWorks RapiFluor-MS N-Glycan Sample Preparation

The following work demonstrates that RFMS labeled glycan samples prepared using this alternative sample preparation scheme are comparable to those produced by the previously published flexible volume procedure. By virtue of its simplification and use of larger volumes, this protocol should be an excellent fit for adoption of RFMS into quality control (QC) environments and automated platforms.

Benefits

RapiFluor-MS glycan labeling procedure with larger volume, simplified liquid transfer to improve ease of use and automatability.

Waters RapiFluor-MS (RFMS) is a novel labeling reagent that provides a fast, efficient, and reproducible sample preparation workflow and unsurpassed fluorescent and MS sensitivity for released N-glycan profiling.^1,2 This initial methodology was designed to accommodate the lowest possible glycoprotein sample concentration and, as result, calls for several low volume (1.2 to 7 μL) liquid transfers. Looking to minimize the impact of pipetting volume inaccuracies, we have redesigned this sample preparation to make pipetting volumes larger (≥10 μL) and thereby reduce the variation in the absolute quantities of analytes and reagents that get delivered during the denaturation, PNGase F deglycosylation, and RFMS labeling steps of the procedure.

The following work demonstrates that RFMS labeled glycan samples prepared using this alternative sample preparation scheme are comparable to those produced by the previously published flexible volume procedure. By virtue of its simplification and use of larger volumes, this protocol should be an excellent fit for adoption of RFMS into quality control (QC) environments and automated platforms.

Comparison of GlycoWorks RapiFluor-MS protocols

The GlycoWorks RapiFluor-MS sample preparation procedure (Table 1) was developed to allow for maximum flexibility with respect to the concentration of the sample being prepared for released N-glycan analysis.³ By altering the addition of water, this method is capable of preparing samples with concentrations as low as 0.66 mg/mL. While this procedure was designed with significant molar excesses of the critical reagents, such as denaturant, enzyme, and the RFMS label, to produce reproducible results,⁴ a potential drawback of this procedure is that several of the aliquoted volumes are well below 10 μL. As such, the methodology is not as amenable for adoption into certain QC laboratories, depending on their internally imposed method requirements, or for use in specific robotic platforms. Pipetted volume accuracy and precision increases with volume and, based on the International Organization for Standardization (ISO) requirements for mechanical pipette accuracy and precision, it is at 10 μL or more that the lowest permissible systematic and random errors are obtained (Figure 1, Adapted from Reference 5). It should be noted that these maximum permissible errors are doubled for the use of multi-channel pipettes. For this reason, some laboratories prefer to avoid procedures with pipetted volumes lower than 10 μL.

To provide a protocol with transfer volumes of 10 μL or more, the standard RFMS sample preparation procedure was reconsidered. The primary changes made to the deglycosylation procedure were that the addition of water was removed, and more dilute solutions of RapiGest SF surfactant and PNGase F were used. The final recommended conditions are presented in Table 2. This revised procedure is designed to give optimal results using a 10 μL sample of glycoprotein at a concentration of 1.5 mg/mL (15 μg of glycoprotein), however, samples that are more or less concentrated can still potentially produce quality results. It should be noted that at significant deviations from the optimal sample quantity, i.e. <5 μg and >30 μg, the labeling reaction can produce undesirable side reactions or low yields, so it is recommended to assess these situations on a case-by-case basis.

The only fundamental difference in this revised procedure is that the concentration of RapiGest SF is slightly higher (1.5%) during the denaturation step versus the previous procedure (1.0%). This increase is not predicted to cause any deleterious effects and may provide some benefit for certain glycoprotein samples that are particularly resistant to denaturation. In the following step, PNGase F deglycosylation, concentrations of the principal components (glycoprotein, RapiGest SF, and PNGase F) are equivalent to the standard, flexible volume procedure.

In modifying the labeling step, the aliquoted amount of the RFMS label solution was decreased from 12 to 10 μL to be consistent with the other lowest pipetted volumes of the procedure. To account for this volume change, the concentration of the RFMS reagent was increased proportionally such that the final ratio of RFMS to glycoprotein remains equivalent. In addition to the protocol using the 1 mL reaction tubes provided in the kit, this revised procedure, like the previous procedure, has also been adapted for use with a 200 μL thermocycler tube. If using a thermocycler with this new QC and automation friendly protocol, it is necessary to divide the final released and labeled glycan sample into two aliquots, or to transfer sample to a larger tube, prior to dilution and SPE clean-up.

Comparing RapiFluor-MS labeled N-glycan profiles

To compare the standard, flexible volume procedure with its newly designed, QC and automation-friendly analog, analyses of the Waters Intact mAb Mass Check Standard were performed. Samples from this murine monoclonal antibody were prepared and analyzed following the two different protocols along with 1 mL sample tubes and single-channel pipettes. A comparison of representative chromatograms for each of these sample preparations are presented in Figure 2. The labeled peaks were integrated and the quantitative results are presented in Figure 3. The glycan species observed in this profile were assigned using online ESI-MS detection with a Xevo G2-XS QTof Mass Spectrometer (Table 3). As can be clearly seen, the two procedures produce both qualitative and quantitative results that are comparable and reproducible for peaks with relative abundances as low as 0.06%.

The GlycoWorks RapiFluor-MS N-glycan sample preparation procedure has been successfully adapted to be more amenable to automation and QC use by adjusting pipetted volumes to ≥10 μL. This supplemental procedure requires a glycoprotein sample concentration of 1.5 mg/mL to obtain optimal results. As an added benefit, the dispensed aliquots of the sample and principal reagents are equivalent in volume (10 μL), thereby providing greater assurance that the relative amounts of these components will be equivalent regardless of the systematic accuracy of the pipetting device that is used, which should result in greater intra-laboratory and inter-laboratory reproducibility.

1. MA Lauber, DW Brousmiche, Z Hua, SM Koza, E Guthrie, P Magnelli, CH Taron, KJ Fountain. Rapid Preparation of Released N-Glycans for HILIC Analysis Using a Novel Fluorescence and MS-Active Labeling Reagent, Application Note [serial on the Internet]. 2015; (720005275en).
   
2. MA Lauber, YQ Yu, DW Brousmiche, Z Hua, SM Koza, P Magnelli, E Guthrie, CH Taron, KJ Fountain. Rapid Preparation of Released N-Glycans for HILIC Analysis Using a Labeling Reagent that Facilitates Sensitive Fluorescence and ESI-MS Detection. Analytical Chemistry 2015.
   
3. GlycoWorks RapiFluor-MS N-Glycan Kit Care and Use Manual (p/n 715004793)
   
4. MA Lauber, MF Morris, DW Brousmiche, SM Koza. Robustness of RapiFluor-MS N-Glycan Sample Preparations and Glycan BEH Amide HILIC Chromatographic Separations, Application Note [serial on the Internet]. 2015; (720005370en).
   
5. ISO 8655-2:2002, pg. 6.