Small Hsp’s (sHsp’s) are an ubiquitous but diverse class of proteins that differ from other Hsp families in that only certain short-sequence motifs, the so-called α-crystallin domains and some sequence in the N-terminal parts, are conserved. Characteristic features in common are their low molecular mass (15–42 kDa), their oligomeric structure ranging from 9 to 50 subunits and their chaperone function in vitro. Additional features attributed to small Hsps range from RNA storage in heat shock granules to inhibition of apoptosis, actin polymerization and contribution to the optical properties of the eye lens in the case of α-crystallin (reviewed inrefs.1 and 2 ). At the moment, it is unclear how these seemingly different functions can be explained by a common mechanism. However, as most of the observed phenomena involve non-native protein, the repeatedly reported chaperone properties of sHsp’ might be a key feature for further understanding of their function.
