PURIFICATION, STRUCTURE AND IN-VITRO MOLECULAR-CHAPERONE ACTIVITY OF ARTEMIA P26, A SMALL HEAT-SHOCK ALPHA-CRYSTALLIN PROTEIN/

Encysted brine-shrimp gastrulae bring their metabolism to a reversible standstill during diapause and quiescence, demonstrating a remarkable resistance to unfavourable environmental conditions. For example, mor tality of Artemia embryos under normal temperature and hydration is ve ry low, even after two years of anoxia, and embryos commonly experienc e complete desiccation as part of their developmental program. Previou s evidence from our laboratories indicated that p26, an abundant low-m olecular-mass cyst-specific protein capable of translocation into the nucleus, may have a protective function in Artemia cysts. p26 was puri fied to apparent homogeneity and a continuous sequence of 141 of its a mino acids was determined by peptide sequencing, revealing that it is a member of the small-heat-shock/alpha-crystallin family of proteins. As determined by molecular-sieve chromatography and sucrose-density-gr adient centrifugation, native p26 is a multimer of about 27 monomers w ith a molecular mass of approximately 700 kDa. Inactivation of citrate synthase was less when the enzyme was heated in the presence rather t han the absence of p26. Additionally, the renaturation of heat-inactiv ated citrate synthase was promoted by p26. These results indicated tha t p26 possesses molecular-chaperone activity, a property of other smal l heat-shock/alpha-crystallin proteins. Our findings demonstrate that p26 has the potential to protect the macromolecular components of Arte mia embryos, either as they encyst or upon exposure to environmental e xtremes. Protection may depend upon the ability of p26 to function as a molecular chaperone.