Heat shock proteins are over-expressed when cells are exposed to heat or stress. Their function is to help other proteins to fold "correctly" into their mature, functional forms and, as such, they are classified as "chaperones". The structures and functions of these proteins will be described in much more detail in section 8 of the PPS course ("The Protein Lifecycle").
Today (21 January), in the School of Crystallography's Monday seminar programme, Maruf Ali from the Institute of Cancer Research in London spoke about his research on the structure of the heat shock protein Hsp90. This protein is found in all kingdoms except for the Archaea; it interacts with many other proteins (known as "client proteins" to help them enter their mature, active structural forms. Hsp90 client proteins include kinases that are important targets for anti-cancer drugs - hence the ICR's interest.
Hsp90 is a three-domain protein. The N-terminal domain binds ATP, which is necessary for the protein's activity; the middle domain binds client proteins; and the C-terminal one is involved in dimerisation. Structures of each domain separately were already known when Maruf started his post-doc a few years ago; each of these domains has a fold in Scop's alpha+beta class. Maruf's work involved solving the structure of a mutated form of the intact protein bound to a co-chaperone, (Ali et al. (2006), Nature 440, 1013-1019; PDB code 2CG9). This structure gives a clear picture of a complex structure, showing how a "lid" of structure closes to enabl the client protein to bind, and supports a previously proposed model in which the N-terminal domain is also involved in dimerisation.
Try downloading the structure, loading it into Jmol or a similar program, and seeing if you can identify the three domains.