CAENORHABDITIS-ELEGANS SMALL HEAT-SHOCK PROTEINS HSP12.2 AND HSP12.3 FORM TETRAMERS AND HAVE NO CHAPERONE-LIKE ACTIVITY

Four 12.2-12.6 kDa small heat-shock proteins (sHSPs) of Caenorhabditis elegans are the smallest known members of the sHSP family. They essen tially comprise the characteristic C-terminal 'alpha-crystallin domain ' of the sHSPs, having a very short N-terminal region, and lacking a C -terminal tail. Recombinant Hsp12.2 and 12.3 are characterized here. F ar-UV CD spectra reveal, as for other sHSPs, predominantly a beta-shee t structure. By gel permeation and crosslinking, they are the first sH SPs shown to occur as tetramers, rather than forming the usual large m ultimeric complexes. Exceptionally, too, both appear devoid of in vitr o chaperone-like abilities. This supports the notion that tetramers ar e the building blocks of sHSP complexes, and that higher multimer form ation, mediated through the N-terminal domains, is a prerequisite for chaperone-like activity. (C) 1998 Federation of European Biochemical S ocieties.