Conformational study of a native monodisulfide bridge analogue of EETI II

Abstract

Trypsin inhibitor EETI II, possessing six cysteines engaged in three disulfide bridges, shares a common structural motif with other proteins of different origins and functions. To understand the principles that govern folding of this largely distributed basic scaffold, mainly composed of a small triple-stranded β-sheet, we have studied different stages in the folding of EETI II. The conformational properties of a synthetic analogue of EETI II possessing only one native (15–27) disulfide bridge were investigated with the combined use of1H NMR and molecular modelling. Although two native-like reverse turns were observed, formation of β-sheet could not be evidenced in the one disulfide analogue, while the motif has been shown to be present in a folding intermediate with two native disulfide bridges (9–21 and 15–27). These results suggest that the structural motif requires stabilisation by two disulfide bridges.