Fragmentation Analysis of rIAPP Monomer, Dimer, and [M rIAPP + M hIAPP ] 5+ Using Collision-Induced Dissociation with Electrospray Ionization Mass Spectrometry

Collision-induced dissociation (CID) combined with electrospray ionization mass spectrometry (ESI-MS) was used to obtain structural information on rat islet amyloid polypeptide (rIAPP) monomers (M) and dimers (D) observed in the multiply charged state in the MS spectrum. MS/MS analysis indicated that the rIAPP monomers adopt distinct structures depending on the molecular ion charge state. Peptide bond dissociation between L 27 and P 28 was observed in the MS/MS spectra of rIAPP monomers, regardless of the monomer molecular ion charge state. MS/MS analysis of the dimers indicated that D 5+ comprised M 2+ and M 3+ subunits, and that the peptide bond dissociation process between the L 27 and P 28 residues of the monomer subunit was also maintained. The observation of (M+ b 27 ) 4+ and (M+ y 10 ) 3+ fragment ions were deduced to originate from the two differ- ent D 5+ complex geometries, the N-terminal and C-terminal interaction geometries, respectively. The fragmentation pattern of the [M rIAPP + M hIAPP ] 5+ MS/MS spectrum showed that the interaction occurred between the two N-terminal regions of M rIAPP and M hIAPP in the heterogeneous dimer (hetero-dimer) D 5+ structure.