Surface-Induced Protein Unfolding in Submicron Electrospray Emitters

Area of Science:

• Analytical Chemistry
• Biochemistry
• Mass Spectrometry

Background:

• Nanoelectrospray ionization (nanoESI) is a technique for generating ions from biomolecules.
• Controlling protein ion charge states is crucial for mass spectrometry analysis.
• Tip size in nanoESI can influence ion formation and charge states.

Purpose of the Study:

• To investigate the effect of nanoESI tip outer diameter on protein ion charging.
• To compare charging efficiency for positively and negatively charged proteins.
• To explore a novel method for producing highly charged protein ions.

Main Methods:

• Comparison of nanoESI using tips with outer diameters ranging from 1.5 μm to 250 nm.
• Analysis of charge-state distributions for proteins with net positive and negative charges.
• Observation of protein unfolding and heme group loss.

Main Results:

• Smaller nanoESI tips (submicron) yield higher charging and additional high-charge-state distributions for positively charged proteins.
• Charge-state distributions for negatively charged proteins are independent of tip size.
• Evidence of protein unfolding and heme loss from myoglobin with smaller tips suggests pre-ionization unfolding.

Conclusions:

• Tip size significantly impacts protein ion charging, particularly for positively charged proteins, due to pre-ionization unfolding.
• This method offers a chemical-free approach to generate highly charged protein ions.
• The findings provide a new strategy for enhancing protein ion generation in mass spectrometry.