The small heat shock protein Hsp22 of Drosophila melanogaster is a mitochondrial protein displaying oligomeric organization

Drosophila melanogaster has four main small heat shock proteins (Hsps), D. melanogaster Hsp22 (DmHsp22), Hsp23 (DmHsp23), Hsp26 (DmHsp26), and Hsp27 ( DmHsp27). These proteins, although they have high sequence homology, show d istinct developmental expression patterns. The function(s) of each small he at shock protein is unknown. DmHsp22 is shown to localize in mitochondria b oth in D. melanogaster 52 cells and after heterologous expression in mammal ian cells. Fractionation of mitochondria indicates that DmHsp22 resides in the mitochondrial matrix, where it is found in oligomeric complexes, as sho wn by sedimentation and gel filtration analysis and by cross-linking experi ments. Deletion analysis using a DmHsp22-EGFP construct reveals that residu es 1-17 and an unknown number of residues between 17-28 are necessary for i mport. Site-directed mutagenesis within a putative mitochondrial motif (WRM AEE) at positions 8-13 shows that the first four residues are necessary for mitochondrial localization. Immunoprecipitation results indicate that ther e is no interaction between DmHsp22 and the other small heat shock proteins . The mitochondrial localization of this small Hsp22 of Drosophila and its high level of expression in aging suggests a role for this small heat shock protein in protection against oxidative stress.