BINDING OF MOLTEN GLOBULE-LIKE CONFORMATIONS TO LIPID BILAYERS - STRUCTURE OF NATIVE AND PARTIALLY FOLDED ALPHA-LACTALBUMIN BOUND TO MODEL MEMBRANES

The effect of membrane binding on the structure and stability of sever al conformers of alpha-lactalbumin was studied by infrared spectroscop y, circular dichroism, and fluorescence spectroscopy, In solution, und er experimental conditions where all conformers interact with negative ly charged membranes, they show significant conformational differences , However, binding to negatively charged membranes, which causes consi derable changes in the structure of these conformers, leads to a remar kably similar protein conformation, The membrane-associated conformati ons are characterized by 1) a high helical content, greater than any o f those found in solution, 2) a lack of stable tertiary structure, and 3) the disappearance of their thermotropic transition, These observat ions indicate that association with negatively charged membranes induc es a conformational change within alpha-lactalbumin to a flexible, mol ten globule-like state.