The small heat-shock chaperone protein, alpha-crystallin, does not recognise stable molten globule states of cytosolic proteins

The small heat-shock protein (sHsp), alpha-crystallin, acts as a molecular chaperone by interacting with destabilised 'substrate' proteins to prevent their precipitation from solution under conditions of stress. alpha-Crystal lin and all sHsps are intracellular proteins. Similarly to other chaperones , the 'substrate' protein is in an intermediately folded, partly structured molten globule state when it interacts and complexes with alpha-crystallin . In this study, stable molten globule states of the cytosolic proteins, ga mma-crystallin and myoglobin, have been prepared. Within the lens, gamma-cr ystallin naturally interacts with alpha-crystallin and myoglobin and alpha- crystallin are present together in muscle tissue. The molten globule states of gamma-crystallin and myoglobin were prepared by reacting gamma-crystall in with glucose 6-phosphate and by removing the haem group of myoglobin. Fo llowing spectroscopic characterisation of these modified proteins, their in teraction with alpha-crystallin was examined by a variety of spectroscopic and protein chemical techniques. In both cases, there was no interaction wi th alpha-crystallin that led to complexation. It is concluded that alpha-cr ystallin does not recognise stable molten globule states of cytosolic 'subs trate' proteins and only interacts with molten globule states of proteins t hat are on the irreversible pathway towards an aggregated and precipitated form. (C) 2000 Elsevier Science B.V. All rights reserved.