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J. Biol. Chem., Vol. 279, Issue 38, 39999-40006, September 17, 2004

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Oligomerization, Chaperone Activity, and Nuclear Localization of p26, a Small Heat Shock Protein from Artemia franciscana^*

Yu Sun, Marc Mansour, Julie A. Crack, Gillian L. Gass, and Thomas H. MacRae

From the Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada

Artemia franciscana embryos undergo encystment, developmental arrest and diapause, the last characterized by profound metabolic dormancy and extreme stress resistance. Encysted embryos contain an abundant small heat shock protein termed p26, a molecular chaperone that undoubtedly has an important role in development. To understand better the role of p26 in Artemia embryos, the structural and functional characteristics of full-length and truncated p26 expressed in Escherichia coli and COS-1 cells were determined. p26 chaperone activity declined with increasing truncation of the protein, and those deletions with the greatest adverse effect on protection of citrate synthase during thermal stress had the most influence on oligomerization. When produced in either prokaryotic or eukaryotic cells the p26 -crystallin domain consisting of amino acid residues 61-152 existed predominantly as monomers, and p26 variants lacking the amino-terminal domain but with intact carboxyl-terminal extensions were mainly monomers and dimers. The amino terminus was, therefore, required for efficient dimer formation. Assembly of higher order oligomers was enhanced by the carboxyl-terminal extension, although removing the 10 carboxyl-terminal residues had relatively little effect on oligomerization and chaperoning. Full-length and carboxyl-terminal truncated p26 resided in the cytoplasm of transfected COS-1 cells; however, variants missing the complete amino-terminal domain and existing predominantly as monomers/dimers entered the nuclei. A mechanism whereby oligomer disassembly assisted entry of p26 into nuclei was suggested, this of importance because p26 translocates into Artemia embryo nuclei during development and stress. However, when examined in Artemia, the p26 oligomer size was unchanged under conditions that allowed movement into nuclei, suggesting a process more complex than just oligomer dissociation.

Received for publication, June 23, 2004

^* This work was supported in part by a Natural Sciences and Engineering Research Council of Canada discovery grant and a regional partnership plan grant including support from the Nova Scotia Health Research Foundation, the Canadian Institutes of Health Research, and the Heart and Stroke Foundation of Nova Scotia (to T. H. M.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Supported by a Nova Scotia Health Research Foundation student research award.

To whom correspondence should be addressed: Dept. of Biology, Dalhousie University, 1355 Oxford St., Halifax, NS B3H 4J1, Canada. Tel.: 902-494-6525; Fax: 902-494-3736; E-mail: tmacrae{at}dal.ca.

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