14 Expression and Function of the Low-molecular-weight Heat Shock Proteins

Abstract

In this chapter, the name sHSP includes all small heat shock proteins, cognate or heat inducible, defined as those proteins possessing the so-called α-crystallin protein domain. In general, the name used for individual sHSP will be hsp xx , where xx corresponds to the two most significant digits of the apparent molecular weight. However, all mammalian sHSP, excluding αA and αB crystallins, are called hsp27 irrespectively of slight interspecies variation in molecular weight, since they represent equivalent proteins, hsp xx from Drosophila melanogaster are called Dm-hsp xx to differentiate these proteins from the mammalian sHSP. I. INTRODUCTION Studies on the cellular response to heat shock and other physiological stresses have identified important families of proteins that are involved not only in cellular protection against these aggressions, but also in essential biochemical processes in unstressed cells. Among the protein families induced by heat shock, much has been learned about the hsp90, hsp70, and hsp60 families; these families accomplish different kinds of chaperonin function(s). This chapter deals with the family of small heat shock proteins (sHSP) which encompasses a large number of related protein species that share some structural features common to the lens protein α-crystallin and are represented in virtually all organisms, excluding perhaps prokaryotes. Neglected for a long time for several reasons including the fact that they did not appear to be as universally conserved as other heat shock proteins and that they were initially not observed in most mammalian cells, this group of heat shock proteins now generates renewed interest. sHSP are expressed...