tailieunhanh - Báo cáo khoa học: Structural and functional roles for b-strand 7 in the a-crystallin domain of p26, a polydisperse small heat shock protein from Artemia franciscana

Oviparous development in the extremophile crustacean,Artemia franciscana, generates encysted embryos which enter a profound state of dormancy, termed diapause. Encystment is marked by the synthesis of p26, a polydis-perse small heat shock protein thought to protect embryos from stress. | iFEBS Journal Structural and functional roles for b-strand 7 in the a-crystallin domain of p26 a polydisperse small heat shock protein from Artemia franciscana Yu Sun Svetla Bojikova-Fournier and Thomas H. MacRae Department of Biology Dalhousie University Halifax NS Canada Keywords a-crystallin domain Artemia franciscana molecular chaperone p26 structure function small heat shock protein Correspondence T. H. MacRae Department of Biology Dalhousie University Halifax NS Canada B3H 4J1 Fax 1 902 4943736 Tel 1 902 4946525 E-mail tmacrae@ Received 5 July 2005 revised 26 December 2005 accepted 5 January 2006 doi Oviparous development in the extremophile crustacean Artemia franciscana generates encysted embryos which enter a profound state of dormancy termed diapause. Encystment is marked by the synthesis of p26 a polydisperse small heat shock protein thought to protect embryos from stress. In order to elucidate structural functional relationships within p26 and other polydisperse small heat shock proteins and to better define the protein s role during diapause amino acid substitutions R110G F112R R114A and Y116D were generated within the p26 a-crystallin domain by site-directed mutagenesis. These residues were chosen because they are highly conserved across species boundaries and molecular modelling indicates that they are part of a key structural interface between dimers. The F112R mutation which had the greatest impact on oligomerization placed two charged residues at the p26 dimer-dimer interface demonstrating the importance of b-strand 7 in tetramer formation. All mutated versions of p26 were less able than wild-type p26 to confer thermotolerance on transformed bacteria and they exhibited diminished chaperone action in three in vitro assays however all variants retained protective activity. This apparent stability of p26 may by prolonging effective chaperone life in vivo enhance embryo stress resistance. All substitutions .