Proteins represent both structural and functional elements of biological organisms, however, their structural and catalytic function is directly linked to the acquisition and maintenance of a complex three-dimensional conformation. A molecular machinery to accomplish protein folding and maintenance in vivo is provided by a variety of molecular chaperones that include both heat shock proteins (Hsps), glucose-regulated proteins (Grps), and a separate class of stress glycoproteins (S-Gps). Different chaperones associate to form functional complexes (chaperone) and work coordinately to accomplish specific functions during the folding of particular proteins. In this review, we will summarize recently acquired new insights into the complexities of chaperones, the current state of S-Gps and their interactions with Hsps, and of specific chaperones that appear to be designed for the folding of cellular glycoproteins. Finally, we discuss the physiological role of chaperones by examining their function in specific cellular processes, namely tumor/host interactions and diseases associated with aberrant prion protein folding.

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