Development of an ion mobility quadrupole time of flight mass spectrometer.

We describe here a new ion mobility capable mass spectrometer which comprises a drift cell for mobility separation and a quadrapole time of flight mass spectrometer for mass analysis--the MoQTOF. A commercial QToF instrument (Micromass UK Ltd., Manchester, UK) has been modified by the inclusion of an additional chamber containing a drift cell and ancillary ion optics. The drift cell is 5.1 cm long made from a copper block and is mounted from a top hat flange in a chamber situated post source optics and prior to the quadapole analyzer. Details of this instrument are provided along with information about how it can be used to acquire mobilities of ions along with their mass to charge ratios. The MoQTOF is used to examine conformations of a series of antimicrobial peptides based on a beta-defensin template. In vivo, these cationic cystine-rich amphiphilic peptides are conformationally restrained by three or more disulfide bridges, although recent findings by several groups have cast doubt on the importance of canonical disulfide pairing to antimicrobial activities. By synthesizing a panel of variants to Defb14 (the murine orthologue of HBD3), we exploit ion mobility to distinguish conformational differences which arise due to disulfide formation and to the hydrophobicity of the peptide sequence. Our gas-phase results are interpreted in terms of the antimicrobial and chemotacic properties of beta-defensins, and this mass spectrometry based approach to discern structure may have a role in future design of novel antibiotics.