Improved in-solution tryptic digestion of proteins in terms of speed and peptide coverage was achieved with the aid of a novel acid-labile anionic surfactant (ALS). Unlike SDS, ALS solubilizes proteins without inhibiting trypsin or other common endopeptidases activity. Trypsin activity was evaluated in the presence of various denaturants; little or no decrease in proteolytic activity was observed in 0.1-1% ALS solutions (w/v). Sample preparation prior to mass spectrometry and liquid chromatography analysis consists of sample acidification. ALS degrades rapidly at low-pH conditions, which eliminates surfactant-caused interference with analysis. Described methodology combines the advantages of protein solubilization, rapid digestion, high peptide coverages, and easy sample preparation for mass spectrometry and liquid chromatography analyses.

N-glycosylation of proteins is now routinely characterized and monitored because of its significance to the detection of disease states and the manufacturing of biopharmaceuticals. At the same time, hydrophilic interaction chromatography (HILIC) has emerged as a powerful technology for N-glycan profiling. Sample preparation techniques for N-glycan HILIC analyses have however tended to be laborious or require compromises in sensitivity. To address these shortcomings, we have developed an N-glycan labeling reagent that provides enhanced fluorescence response and MS sensitivity for glycan detection and have also simplified the process of preparing a sample for analysis. The developed labeling reagent rapidly reacts with glycosylamines upon their release from glycoproteins. Within a 5 min reaction, enzymatically released N-glycans are labeled with this reagent comprised of an NHS-carbamate reactive group, a quinoline fluorophore, and a tertiary amine for enhancing ESI+ MS ionization. To further expedite the released N-glycan sample preparation, rapid tagging has been integrated with a fast PNGase F deglycosylation procedure that achieves complete deglycosylation of a diverse set of glycoproteins in approximately 10 min. Moreover, a technique for HILIC-SPE of the labeled glycans has been developed to provide quantitative recovery and facilitate immediate HILIC analysis of the prepared samples. The described approach makes it possible to quickly prepare N-glycan samples and to incorporate the use of a fluorescence and MS sensitivity enhancing labeling reagent. In demonstration of these new capabilities, we have combined the developed sample preparation techniques with UHPLC HILIC chromatography and high sensitivity mass spectrometry to thoroughly detail the N-glycan profile of a monoclonal antibody.

The gas-phase structures of five five-carbon monosaccharides (D-ribose, D-lyxose, 2-deoxy-D-ribose, D-xylose, and D-arabinose) were studied via ion-molecule reactions with dimethoxyphosphenium ion and 1,3-dioxolane-2-phosphenium ion in a Fourier transform ion cyclotron resonance mass spectrometer. These reagent ions have been earlier demonstrated to be sensitive to the three-dimensional structures of diastereomeric vicinal diols. They were found to display unique reactivity toward each monosaccharide. The results indicate that the gaseous monosaccharides are cyclic molecules. On the basis of a comparison of the reactions of monosaccharides introduced into the gas phase via two different methods, laser-induced acoustic desorption (LIAD) and thermal desorption, the monosaccharides are concluded to maintain their crystalline structure, a pyranose form, throughout the evaporation procedure. For all the monosaccharides in this study except for D-lyxose, the lowest-energy structure found computationally using density functional theory (B3LYP/6-311++G(d,p)) is a pyranose form that lies at least 1.7 kcal/mol lower in energy than the corresponding lowest-energy furanose form. For D-lyxose, however, a furanose form was calculated to be lower in energy than the pyranose form albeit only by 0.1 kcal/mol. These computational results suggest that a pyranose form indeed is likely to be the dominant form of the monosaccharides in the gas phase. Several possible factors controlling the relative stability of each monosaccharide isomer in the gas phase were examined computationally. The order of importance of these factors in determining the relative stabilities was found to be as follows; intramolecular hydrogen bonding interactions . anomeric > steric (axial/equatorial) factors . ∆2 effect.

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Figure 3. Normalized MALDI-TOF spectra of bacteriorhodopsin tryptic peptides. (A) ALS was not degraded, surfactant is present in the sample. (B) ALS was degraded, pellet isolated and the hydrophobic peptides extracted by isopropanol. The inset mass spectra were acquired in reflectron mode; ACTH was used for internal mass calibration. The mass spectra in the range m/z 2500-6000 were acquired in linear mode; insulin was used as internal calibrant.