HSP27: Protein Type

Hsp27 is a highly phosphorilable, ATP-independent protein. It has a characteristic C-terminal ‘α-crystallin domain’ of 80–100 residues and contains short consensus sequences that are highly conserved from prokaryotes to eukaryotes. There are, in addition, some positions that clearly distinguish animal from non-animal Hsps. The α-crystallin domain is predicted to consist of two hydrophobic β-sheet motifs (Figure 1), separated by a hydrophilic region of variable length. The N-terminus with its WD/EPF-region is essential for the development of high molecular oligomers²¹, exclusively have chaperone activity in vitro. Hsp27-oligomers probably consist of stable dimers, which are formed by two α-crystallin-domains of neighboring monomers ²². The stable dimers aggregate to tetramers and finally form unstable oligomers. The oligomerization depends on the physiology of the cells, the phosphorylation status of Hsp27 and the exposure to stress. Thus, it is expected that the oligomerization status is connected with the chaperone activity: aggregates of large oligomers have high chaperone activity, whereas dimers have no chaperone activity²².