Investigation of protein‐protein noncovalent interactions in soybean agglutinin by electrospray ionization time‐of‐flight mass spectrometry

Abstract

Noncovalent interactions in soybean agglutinin (SBA) were studied on an electrospray ionization (ESI) time-of-flight mass spectrometer constructed recently at the University of Manitoba. The high m/z range and high sensitivity of the instrument together with mild ESI interface conditions turned out to be ideal for detecting this noncovalently bonded tetrameric protein (MW ∼ 116 000 Da) in low charge states (z=23 to 27). By altering the acetonitrile content of the SBA solutions it was shown that the observed SBA tetramers are due to structurally specific noncovalent associations in solution. Octamers and dodecamers (MW ∼ 350 000 Da) were also detected. Information on the quaternary structure of the tetramers was obtained by analyzing the fragment-ion spectrum resulting from the collision-induced dissociation of the tetramer ions.