Simplifying the exoglycosidase digestion/MALDI-MS procedures for sequencing N-linked carbohydrate side chains

Area of Science:

• Glycobiology
• Analytical Chemistry
• Mass Spectrometry

Background:

• Exoglycosidase digestion combined with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is crucial for N-linked carbohydrate side chain sequencing in glycoproteins.
• Conventional enzymatic buffers interfere with MALDI-MS analysis, necessitating a desalting step prior to mass spectrometry.
• This pre-analysis desalting step adds complexity and potential sample loss to the glycoprotein analysis workflow.

Purpose of the Study:

• To develop an improved method for analyzing glycoprotein N-linked carbohydrate side chains.
• To eliminate the need for a desalting step between exoglycosidase digestion and MALDI-MS analysis.
• To identify compatible buffer systems that maintain enzyme activity and specificity for direct mass spectrometry analysis.

Main Methods:

• Investigated the use of 25 mM ammonium acetate solutions at appropriate pH as replacements for standard exoglycosidase digestion buffers.
• Performed exoglycosidase digestion of N-linked glycans using the optimized ammonium acetate buffer system.
• Analyzed the resulting digestion products directly using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) without an intermediate desalting step.

Main Results:

• Demonstrated that 25 mM ammonium acetate solutions are compatible with exoglycosidase digestion.
• Showed that direct MALDI-MS analysis of the digestion mixture is feasible without prior desalting when using ammonium acetate buffers.
• Confirmed that common exoglycosidases maintain significant activity and specificity in 25 mM ammonium acetate buffers.

Conclusions:

• A simplified and more efficient workflow for N-linked glycan sequencing using exoglycosidase digestion and MALDI-MS has been established.
• The use of ammonium acetate buffers streamlines the analytical process by removing the requirement for desalting.
• This optimized method enhances the utility of MALDI-MS for comprehensive glycoprotein glycan analysis.