NMR study of the reconstitution of the beta-sheet of thioredoxin by fragment complementation.

The study of complementary protein fragments is thought to be generally useful to identify early folding intermediates. A prerequisite for these studies is the reconstitution of the native-like structure by fragment complementation. Structural analysis of the complementation of the domain-sized proteolytic fragments of E. coli thioredoxin, using a combination of H-exchange and 2D NMR experiments as a fingerprint technique, provide evidence for the extensive reconstitution of a native beta-sheet, with local conformational adjustments near the cleavage site. Remarkably, the antiparallel beta-strand between the fragments shows a native-like protection of the amide protons to solvent exchange. Our results indicate that these fragments can be useful to study the early events in the still little understood formation of beta-sheets.