Multiplex Detection of Protein Toxins Using MALDI-TOF-TOF Tandem Mass Spectrometry: Application in Unambiguous Toxin Detection from Bioaerosol

Protein toxins, such as botulinum neurotoxins (BoNTs), Clostridium perfringens epsilon toxin (ETX), staphylococcal enterotoxin B (SEB), shiga toxin (STX), and plant toxin ricin, are involved in a number of diseases and are considered as potential agents for bioterrorism and warfare. From a bioterrorism and warfare perspective, these agents are likely to cause maximum damage to a civilian or military population through an inhalational route of exposure and aerosol is considered the envisaged mode of delivery. Unambiguous detection of toxin from aerosol is of paramount importance, both for bringing mitigation protocols into operation and for implementation of effective medical countermeasures, in case a “biological cloud” is seen over a population. A multiplex, unambiguous, and qualitative detection of protein toxins is reported here using tandem mass spectrometry with MALDI-TOF-TOF. The methodology involving simple sample processing steps was demonstrated to identify toxins (ETX, Clostridium perfringes phospholipase C, and SEB) from blind spiked samples. The novel directed search approach using a list of unique peptides was used to identify toxins from a complex protein mixture. The bioinformatic analysis of seven protein toxins for elucidation of unique peptides with conservation status across all known sequences provides a high confidence for detecting toxins originating from any geographical location and source organism. Use of tandem MS data with peptide sequence information increases the specificity of the method. A prototype for generation of aerosol using a nebulizer and collection using a cyclone collector was used to provide a proof of concept for unambiguous detection of toxin from aerosol using precursor directed tandem mass spectrometry combined with protein database searching. ETX prototoxin could be detected from aerosol at 0.2 ppb concentration in aerosol.