We report here the near complete assignments of native bovine PI3-SH3 domain, which has been a model system for protein folding, misfolding and amyloid fibril formation. The use of (13)C-detected protonless NMR spectroscopy is instrumental in assigning the spin system of the proline residue at the C-terminus in addition to the missing resonances in proton-based NMR spectra due to rapid solvent exchange. It also helps assign the resonances of all three proline amine nitrogen nuclei, which are underrepresented in the database. Comparison of the backbone (13)C resonances of PI3-SH3 in its native and amyloid fibril states shows that the aggregation of PI3-SH3 is accompanied by major conformational rearrangements.