LOCAL STRUCTURAL PREFERENCES IN THE ALPHA-LACTALBUMIN MOLTEN GLOBULE

Molten globules have been proposed to be general intermediates in prot ein folding. Despite numerous studies, a detailed description of the s tructure of a molten globule remains elusive. Recently, we showed that the molten globule formed by the helical domain of alpha-lactalbumin (alpha-LA) has a nativelike backbone topology. Here we probe local str uctural preferences in the helical domain of the alpha-LA molten globu le by analyzing a set of native and nonnative single disulfide bond va riants using a combination of circular dichroism spectroscopy and dete rmination of the equilibrium constant for disulfide bond formation. We find that the region surrounding the 28-111 disulfide bond has a high preference to adopt a native-like structure. Formation of other nativ e or nonnative disulfide bonds is significantly less favorable. Our re sults suggest that molten globules contain regions with varying degree s of specificity for native-like structure and that the core region su rrounding the 28-111 disulfide bond plays an important role in alpha-L A folding by stabilizing the molten globule intermediate.