Spectroscopic characterization of heat-induced nonnative beta-lactoglobulin monomers.
Previous studies have shown that two altered monomeric species were formed in the early steps of thermal denaturation of bovine beta-lactoglobulin (beta-lg), the well-known Cys121-exposed intermediate (Mcys121), and a new, stable monomer with exposed nonnative Cys119 (Mcys119). In this study, circular dichroism and fluorescence spectroscopies were used to characterize the structural features of these molecules. The structural characteristics of MCys121 after heating and cooling cycles are similar to those of native beta-lg. In contrast, Mcys119 monomer exhibits some characteristics of the well-known molten-globule state. Combined with other published data, these results indicate that heating induces at least two molten globule-like states of beta-lg, a highly reactive Mcys121 that returns to native state after cooling, and a less-reactive Mcys119 that is trapped and stabilized in a molten globule-like state by nonnative disulfide bond.
Croguennec
Thomas
T
Unité Mixte de Recherche Ecole Nationale Supérieure Agronomique-Institut National de Recherche Agronomique, 35 042 Rennes, France. Thomas.Croguennec@agrorennes.educagri.fr
Mollé
Daniel
D
Mehra
Raj
R
Bouhallab
Saïd
S
D000818:Animals; D002417:Cattle; D003545:Cysteine / Q000032:analysis / Q000737:chemistry; D005033:Ethylmaleimide / Q000737:chemistry; D006358:Hot Temperature; D007782:Lactoglobulins / Q000032:analysis / Q000737:chemistry*; D010449:Peptide Mapping; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013057:Spectrum Analysis
D007782:Lactoglobulins; D003545:Cysteine; D005033:Ethylmaleimide