The interaction of the molecular chaperone, alpha-crystallin, with molten globule states of bovine alpha-lactalbumin.
Small heat shock proteins function in a chaperone-like manner to prevent the precipitation of proteins under conditions of stress (e. g. heat). alpha-Crystallin, the major mammalian lens protein, is a small heat shock protein. The mechanism of chaperone action of these proteins is poorly understood. In this paper, the conformational state of a protein when it forms a high molecular weight complex with alpha-crystallin is investigated by examining, using NMR spectroscopy and size exclusion high performance liquid chromatography, the interaction of alpha-crystallin with alpha-lactalbumin and its various intermediately folded (molten globule) states. The complex is formed following reduction of alpha-lactalbumin by dithiothreitol in the presence of alpha-crystallin, and this interaction has been monitored in real time by 1H NMR spectroscopy. It is concluded that alpha-crystallin interacts with a disordered molten globule state of alpha-lactalbumin while it is on an irreversible pathway toward aggregation and precipitation. alpha-Crystallin does not interact, however, with molten globule states of alpha-lactalbumin that are stable in solution, e.g. the reduced and carboxyamidated species. It is proposed that alpha-crystallin distinguishes between the various molten globule states of alpha-lactalbumin on the basis of the lifetimes of these states, i.e. the protein must be in a disordered molten globule state for a significant length of time and on the pathway to aggregation and precipitation for interaction to occur.
Lindner
R A
RA
Department of Chemistry, The University of Wollongong, Northfields Avenue, Wollongong, New South Wales 2522, Australia.
Kapur
A
A
Carver
J A
JA
D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D003459:Crystallins / Q000378:metabolism*; D007768:Lactalbumin / Q000737:chemistry / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D018832:Molecular Chaperones / Q000378:metabolism*; D008970:Molecular Weight; D009994:Osmolar Concentration; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding
D003459:Crystallins; D018832:Molecular Chaperones; D007768:Lactalbumin