The Chaperone-like α-Crystallin Forms a Complex Only with the Aggregation-Prone Molten Globule State of α-Lactalbumin

Abstract

The chaperone-like α-crystallin prevents aggregation of several proteins by interacting with their non-native states. α-Lactalbumin adopts different non-native states under different experimental conditions. We have investigated the interaction of α-crystallin with three non-identical non-native states, using fluorescence, circular dichroism, and gel filtration chromatography. The compact molten globule state of apo-α-lactalbumin in tris buffer does not interact with α-crystallin. The expanded, flexible molten globule-like state of reduced apo-α-lactalbumin (formed at pH 7.2) also does not interact with α-crystallin. Only the aggregation-prone non-native state of reduced apo-α-lactalbumin formed at pH 6.0 interacts with α-crystallin to form a stable complex. The α-crystallin bound reduced apo-α-lactalbumin exhibits properties similar to those of a molten globule. Our results show that α-crystallin interacts only with the aggregation prone molten globule state of reduced apo-α-lactalbumin but not with the other non-aggregating molten globule states of the protein.