The lack of chaperonelike activity of Caenorhabditis elegans Hsp12.2 cannot be restored by domain swapping with human alpha B-crystallin

The small heat shock proteins Hsp 12.2 and (alphaB-crystallin differ in tha t the former occurs as tetramers, without chaperonelike activity, whereas t he latter forms multimers and is a good chaperone. To investigate whether t he lack of chaperone activity of Hspl 2.2 is primarily due to its tetrameri c structure or rather to intrinsic sequence features, we engineered chimeri c proteins by swapping the N-terminal, C-terminal, and tail regions of Hsp1 2.2 and alphaB-crystallin, designated as n-c-t and N-C-T, respectively. Thr ee of the chimeric sHsps, namely N-c-T, n-c-T, and N-C-t, showed nativelike secondary and quaternary structures as measured by circular dichroism and gel permeation chromatography. Combining the conserved a-crystallin domain of Hsp12.2 with the N-terminal and tail regions of (YB-crystallin (N-c-T) r esulted in multimeric complexes, but did not restore chaperonelike activity . Replacing the tail region of Hsp12.2 with that of alphaB-crystallin (n-c- T) did not alter the tetrameric structure and lack of chaperone activity. S imilarly, providing (alphaB-crystallin with the tail of Hsp12.2 (N-C-t) did not substantially influence the multimeric complex size, but it reduced th e chaperoning ability, especially for small substrates. These results sugge st that the conserved alpha -crystallin domain of Hsp12.2 is intrinsically unsuitable to confer chaperonelike activity and confirms that the tail regi on in alphaB-crystallin modulates chaperonelike capacity in a substrate-dep endent manner.