Mapping Protein Interfaces by Chemical Cross-Linking and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: Application to a Calmodulin/Adenylyl Cyclase 8 Peptide Complex

Chemical cross-linking—an established technique in protein chemistry—has re-emerged, in combination with mass spectrometric analysis of the reaction products, as a valuable tool to identify interacting amino acid sequences in protein complexes. In the present study, we are mapping the interface of the calcium-dependent complex between calmodulin (CaM) and a peptide derived from the C-terminal region of adenylyl cyclase 8 (AC 8). Cross-linking reactions are performed using the two amine-reactive, isotope-labeled ( d0 and d4) cross-linkers BS3 ( bis[sulfosuccinimidyl]suberate) and BS2G ( bis[sulfosuccinimidyl]glutarate) as well as the “zero-length” cross-linker (EDC, ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride). After separation of the cross-linking reaction mixtures by one-dimensional gel electrophoresis (sodium dodecyl sulphate polyacrylamide gel) and in-gel digestion of the cross-linked complexes, the resulting peptide mixtures are analyzed by nano-high-performance liquid chromatography/nano-electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The identified intermolecular cross-linking products will give further insight into calmodulin/adenylyl cyclase 8 interaction.