Studies of conformational features of fragments SNase(111-143) and SNase(118-143) and segment E122-K136 in 1-139 fragment (SNase139) suggest that the high intrinsic helical propensity can drive segment E122-K136 fold into a stable helix only when the segments V111-H121 and L137-D143 flanked on segment E122-K136 in staphylococcal nuclease (SNase) have stable folding.