Disulfide bond formation between the N-terminal region of P56(LCK) and the cytoplasmic domain of CD8 studied by electrospray ionization and matrix-assisted desorption ionization time-of-flight mass spectrometry

Masses of the complexes formed between the C-terminal region of CD8 alpha (CD8 alpha C) and the N-terminal region of p56(lck) (p56(lck)N) were measured by using Electrospray Ionization (ESI) and Matrix-Assisted Laser Desorption/Ionization (MALDI) Mass Spectrometry (MS). The two peptides were incubated with various metal ions, Zn++, Cd++, Co++, Fe++ and Ca++. The complex formed from the incubation did not contain any metal ions. Instead, its mass suggested that the complex was formed by two disulfide bonds. The fact that the incubation of the complex with Dithiothreitol broke the complex confirmed into monomers that the complex was formed through disulfide bonds. The only disulfide-mediated complex formed was hetero-dimer (CD8 alpha C-p56(lck)N) and none of homo-dimers (CD8 alpha C-CD8 alpha C or p56(lck)N-p56(lck)N) were observed from ESI and MALDI-TOF mass spectrometry.