Intact and top-down characterization of biomolecules and direct analysis using infrared matrix-assisted laser desorption electrospray ionization coupled to FT-ICR mass spectrometry

Abstract

We report the implementation of an infrared laser onto our previously reported matrix-assisted laser desorption electrospray ionization (MALDESI) source with ESI post-ionization yielding multiply charged peptides and proteins. Infrared (IR)-MALDESI is demonstrated for atmospheric pressure desorption and ionization of biological molecules ranging in molecular weight from 1.2 to 17 kDa. High resolving power, high mass accuracy single-acquisition Fourier transform ion cyclotron resonance (FT-ICR) mass spectra were generated from liquid- and solid-state peptide and protein samples by desorption with an infrared laser (2.94 mum) followed by ESI post-ionization. Intact and top-down analysis of equine myoglobin (17 kDa) desorbed from the solid state with ESI post-ionization demonstrates the sequencing capabilities using IR-MALDESI coupled to FT-ICR mass spectrometry. Carbohydrates and lipids were detected through direct analysis of milk and egg yolk using both UV- and IR-MALDESI with minimal sample preparation. Three of the four classes of biological macromolecules (proteins, carbohydrates, and lipids) have been ionized and detected using MALDESI with minimal sample preparation. Sequencing of O-linked glycans, cleaved from mucin using reductive beta-elimination chemistry, is also demonstrated.

Figure 1

Schematic of solid-state IR-MALDESI with ESI post-ionization and representative mass spectrum of bovine cytochrome c mixed with succinic acid.

Figure 2

Schematic of liquid-state IR-MALDESI with ESI post-ionization and representative mass spectrum of bovine cytochrome c mixed with 10% glycerol.

Figure 3

Top-down sequencing of equine myoglobin using solid-state IR-MALDESI with ESI post-ionization.

Figure 4

Liquid-state MALDESI mass spectrum of bovine milk with no sample preparation using: (a) UV laser desorption, (b) IR laser desorption with ESI post-ionization and egg yolk using (c) UV laser desorption with DHB and (d) IR laser desorption with no sample preparation with ESI post-ionization.

Figure 5

Liquid-state IR-MALDESI of O-linked glycans cleaved from mucin using reductive β-elimination chemistry. Circles denote sodium adducted glycans; diamonds denote protonated glycans. Inset shows MS/MS sequencing of glycan with m/z = 1179.4386.