Biological systems are characterized by a form of molecular recycling – and proteins do not escape this fate. In particular, unneeded or damaged proteins biochemically marked for destruction undergo controlled degradation by having their peptide bonds broken by proteasomes. Recently, scientists at the Max-Planck Institute of Biochemistry in Germany used cryo-electron microscopy (cryo-EM) single particle analysis and molecular dynamics techniques to map the Saccharomyces cerevisiae 26S proteasome. (Cryo-EM is a form of transmission electron microscopy where the sample is studied at cryogenic temperatures, which unlike X-ray crystallography allows researchers to observe specimens in their native environment without the need for staining or fixing. S. cerevisiae is the yeast species commonly known as baker's or brewer's yeast.) The researchers then used this map to build a near-atomic resolution structural model of the proteasome. The Max Planck team showed that cryo-electron microscopy allowed them to successfully model the 26S core complex where X-ray crystallography studies conducted over the past 20 years have not.
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