The native state 1H, 15N resonance assignment of 123 of the 128 nonproline residues of canine milk lysozyme has enabled measurements of the amide hydrogen exchange of over 70 amide hydrogens in the molten globule state. To elucidate the mechanism of protein folding, the molten globule state has been studied as a model of the folding intermediate state. Lysozyme and α-lactalbumin are homologous to each other, but their equilibrium unfolding mechanisms differ. Generally, the folding mechanism of lysozyme obeys a two-state model, whereas that of α-lactalbumin follows a three-state model. Exceptions to this rule are equine and canine milk lysozymes, which exhibit a partially unfolded state during the equilibrium unfolding; this state resembles the molten globule state of α-lactalbumin but with extreme stability. Study of the molten globules of α-lactalbumin and equine milk lysozyme showed that the stabilities of their α-helices are similar, despite the differences in the thermodynamic stability of their molten globule states. On the other hand, our hydrogen exchange study of the molten globule of canine milk lysozyme showed that the α-helices are more stabilized than in α-lactalbumin or equine milk lysozyme and that this enhanced stability is caused by the strengthened cooperative interaction between secondary structure elements. Thus, our results underscore the importance of the cooperative interaction in the stability of the molten globule state. (C) 2000 Wiley-Liss, Inc.
|Number of pages
|Proteins: Structure, Function and Genetics
|Published - Sept 1 2000
All Science Journal Classification (ASJC) codes
- Structural Biology
- Molecular Biology