Identification of a site of Hsp27 binding with Hsp27 and αB-crystallin as indicated by the yeast two-hybrid system

The small heat-shock proteins (sHsp), including Hsp27 and alpha B-crystallin, usually form large oligomers in cells. It has been suggested that the sHsp form oligomers by binding either a conserved C-terminal amino acid sequence or the less conserved N-terminal region. However, the site of binding has not been precisely determined. We used the yeast two-hybrid system to investigate binding of full-length rat Hsp27 or fragments of Hsp27 to full-length rat Hsp27 or alpha B-crystallin molecules. A series of cDNAs coding for fragments of Hsp27 were generated and ligated with the coding sequence for the binding domain of the yeast Gal4p transcription factor. These cDNAs were each transfected into yeast that had been transfected to express full-length rat Hsp27 or alpha B-crystallin fused with the DNA binding domain of Gal4p. Yeast cells transfected with both plasmids were assayed, by both a beta-galactosidase (beta-gal) filter assay and a quantitative liquid assay, for activation of Gal4p-driven beta-gal expression. Results indicated that the N-terminal domain of Hsp27 consisting of amino acids 1-124 did not bind to Hsp27 or alpha B-crystallin. The predominant Hsp27-Hsp27/alpha B-crystallin binding domain was the conserved C-terminal region consisting of amino acids 141-206, particularly amino acids 141-176. (C) 1999 Academic Press.