Heat shock protein HSP33
Escherichia coli (bacteria)
Stresses of various kinds are a common occurrence caused by environmental factors like heat, toxic particles or lack of oxygen. Cell in the body respond to such stress by increasing the amount of certain proteins that are naturally present in the cell, the so-called heat shock proteins (HSP). Despite their name heat shock proteins are not just involved in response to heat shock, they have several natural functions. One of these functions is to act as chaperonins. In this function they help eliminate misfolded proteins and help them refold, if possible. Usually heat shock proteins are contained within a cell. When heat shock proteins are found outside of cells, it means that diseased cells have broken down completely. The occurrence of heat shock proteins outside the cell can thus be seen as a signal to the immune system. Heat shock proteins actually were discovered by the fact that mice can be vaccinated against cancer, eliciting an immune response. It was then found through systematic search that the factor responsible for this are heat shock proteins. This is how they were first discovered.
The heat shock protein seen here is a biological dimer. However its dimer symmetry is so high that the symmetry of the crystal and that of the HSP coincide. Hence the basic building block of the crystal contains only one monomer. The monomer contains two domains, one compact domain and a small domain containing two helices and a long loop. The compact domain has a peculiar geometry. Two beta sheets, one 4-stranded and the other one 5-stranded, surround one long helix in the center of this domain, like a sandwich with a sausage inside. The molecule also show two sulfate ions and a larger molecule next to the central helix, called MES or 2-(N-morpholino)- ethanesulfonic acid. They are not related to the function of the protein, but just happened to be in there as a result of the crystallization mix. It is however interesting to see how MES actually binds within HSP and such observations can sometimes be useful in the search for new drugs, even if they are accidental.
Protein Data Bank (PDB)
Vijayalakshmi, J. Mukhergee, M.K. Graumann, J. Jakob, U. Saper, M.A.; "The 2.2 angstroms crystal structure of Hsp33: a heat shock protein with redox-regulated chaperone activity."; Structure; (2001) 9:367-375 PubMed:11377197.
author: Arno Paehler