Online saw-bioaffinity-mass spectrometry : new tool for simultaneous detection, structure determination and affinity quantification of protein-ligand interactions from biological material

Abstract

Bioaffinity analysis using biosensors such as surface plasmon resonance has become an established technique for the detection and quantification of biomolecular interactions. However, a principal limitation of biosensors is their lack of providing structure analysis of affinity-bound ligands. We have developed an online combination of a surface acoustic wave (SAW) biosensor with electrospray ionization mass spectrometry (SAW-ESI-MS) that enables the simultaneous structure determination and affinity quantification of biopolymer ligands, dissociated from the biopolymer- ligand complex on a gold chip. Key tool of the SAW-MS combination is an interface that provides sample concentration and in-situ desalting for the MS analysis of the ligand eluate. Recent applications of the online bioaffinity- MS show broad bioanalytical potential for direct interaction studies from biological material, as diverse as antigen-antibody and lectin- carbohydrate complexes; affinity binding constants (KD) are determined from milli- to nanomolar ranges [1,2]. Moreover, we report here first applications of the online- SAW- MS to the direct top-down structural characterization of proteolytic intermediates and oligomers in the aggregation of Parkinson’s Disease key protein, alpha-synuclein (αSyn) [3] from brain homogenate.