The degradation of proteins and other macromolecules in cells is vital to survival. Disruption of this process can result in serious disease. The research group of Professor Thomas Jentsch (Leibniz Institute for Molecular Pharmacology, FMP/ Max Delbrck Center for Molecular Medicine, MDC, Berlin-Buch) has now succeeded in identifying an essential cellular process necessary for the transport and degradation of macromolecules in endosomes and lysosomes, respectively. In two studies published in the same issue of the journal Science, they showed that contrary to scientific consensus the function of these tiny cell organelles not only depends on the pH, but also on chloride ion accumulation in their interior (Science 11 June 2010, Vol. 328. no. 5984, pp. 1398-1401, DOI: 10.1126/science.1188070; pp. 1401-1403, DOI: 10.1126/science.1188072; originally published in Science Express on 29 April 2010)*.
Proteins are the building blocks and machines of life. Tens of thousands of them are present in each cell, where they perform essential tasks for the organism. Once they have fulfilled their function, they must be degraded to avoid causing damage. One way in which proteins can be degraded is via the digestion processes inside tiny cellular organelles, the lysosomes. The transport of the proteins destined for degradation to these cellular "trash bins" is partly carried out by endosomes, which deliver proteins from the cell surface to the cell interior.
The functionality of both endosomes and lysosomes depends on the ion concentration within their membrane-enclosed interior. In particular, an important role is ascribed to a high concentration of hydrogen ions, i.e. an acidic pH, inside those organelles.
The two studies by Dr. Stefanie Weinert, Dr. Gaia Novarino and Professor Thomas Jentsch focus on two ion transport proteins, the chloride transporters ClC-5 and ClC-7. These are located in the membrane of endosomes and/or lys
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