Many unrelated proteins share identical short peptide sequence but adopt different conformations. Structural transformation that occurs in the process of protein folding and functioning is of great significance in biological organisms. The structural transformation of peptide segment in the process of serpin and EF-Tu inactivation, hemagglutinin activation, protease maturation, subunit assembly and protein amyloidosis is reviewed and its implication for the understanding of protein folding and “conformational diseases” is also discussed.