Infrared Laser Desorption and Electrospray Ionisation of Non-Covalent Protein Complexes: Generation of Intact, Multiply Charged Species

We present a novel method enabling the infrared laser desorption and electrospray ionisation (ESI) of protein complexes in their native state. Using this method, we demonstrate the surprising generation of intact, multiply charged ions of myoglobin, non-covalent haemoglobin complex, and intact immunoglobulin G antibody in their native states. The observation of a surviving population of intact non-covalent complexes is characteristic of the low internal energy build-up experienced during both laser desorption from solution and subsequent ionisation. Compared to conventional nano-ESI, this approach yielded slightly lower average charge states suggesting additional maintenance of tertiary structure during desorption and ionisation, and is more tolerant to salts enabling simpler sample purification procedures. This approach may enable the development of high-throughput native-MS methods capable of analysing the composition and sequence of multiple macromolecular samples per minute.