Another interesting case study is found with the growth factors where we see dimers formed in 3 different ways, corresponding to two-fold axes in different directions. Examples of symmetrical enzyme multimers in the form usually found in cells have been especially prepared and archived at Brookhaven in a directory dedicated to these biological units. There are other examples where dimerisation is necessary to actually create the active site of the enzyme in question. The molecular machinery of the cell and indeed of assemblies of cells, rely on or are controlled by large multimeric assemblies of proteins, nucleic acids, lipids, and sugars. Fiberous proteins are very elongated and interact to form long strong fibers.
Filamentous proteins are globular and assemble into long tubules or filaments.
Viruses are large assemblies of proteins, nucleic acids and sometimes lipids. They perform a wide range of functions from replication to membrane fusion which are made possible only by their diverse multimeric nature. If you have MAGE installed and configured for Chemical MIME, you can view the Branden and Tooze , Protein Science and Protein Tourist Kinemages , some of which are relevant to this material. Again, refer to the Technology Page if necessary. There are some links to appropriate Kinemages within this chapter.