Human Hsp40/DnaJ proteins comprise a large protein family, members of which feature the J domain (named after the bacterial DnaJ protein) (1). The J-domain spans the first 75 N-terminal amino acids and is separated from the C-terminal by a glycine/phenylalanine-rich domain (2). There are two main types of Hsp40; type 1 DNAJ proteins including HDJ2 and yeast YdjI; type II includes yeast Sis1 and human Hdj1. Whereas type I possesses a zinc finger domain which helps in the function of protein folding. (3, 4), type II does not.
Members of the Hsp40/DnaJ family play diverse roles in many cellular processes, such as folding, translocation, degradation and assembly of multi-protein complexes. Hsp40 stimulates the ATPase activity of Hsp70 which in turn causes conformational changes of the unfolded proteins (5, 6). The Hsp40-Hsp70-unfolded protein complex further binds to co-chaperones Hip, Hop and
HSP90 which leads to protein folding, or components of protein degradation machinery CHIP and BAG-1 (7).