The study of protein-ligand interactions at high m/z by electrospray ionization mass spectrometry
- Pacific Northwest Lab., Richland, WA (United States)
A wide variety of biological noncovalent systems have been found to be preserved through the ESI process and detected by mass spectrometry. Transfer of these complexes into the gas phase relies on the careful control of the atmosphere-vacuum interface conditions. In certain cases, the typical ESI solution conditions, i.e. acidic or basic, employed for detection of ions within the conventional m/z range of quadrupole instruments have proven to be destructive to higher order structural elements of noncovalent complexes. Utilizing aqueous solutions closer to neutral pH is more amenable to preserving multisubunit proteins. However, these solution conditions result in a decreased amount of charging for proteins in the gas phase and a narrower charge state distribution, presumably due to a more compact quaternary structure. In these instances, the use of an instrument capable of extended m/z detection (>3,000) may be required to observe ions corresponding to intact multimeric proteins. The noncovalent proteins avidin (M{sub r} {approximately} 64,000) and streptavidin (M{sub r} {approximately} 54,000) are each composed of four identical subunits which associate into the active form. These tetrameric species share an exceptionally high affinity for biotine (M{sub r} = 224 Da), and the protein-ligand complex of four biotins binding to the quaternary structure of either protein represents one of the strongest known noncovalent biochemical interactions (K{sub D} {approximately} 10{sup -15} M). In order to detect the quaternary structure of these multisubunit proteins, as well as the intact protein-ligand complexes, a low rf frequency extended m/z range ({approximately}45,000) quadrupole mass spectrometer was employed.
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 61876
- Report Number(s):
- CONF-9405234--
- Country of Publication:
- United States
- Language:
- English
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