oats around in the cytoplasm. Not unlike white blood cells, they can engulf larger proteins or even whole cell organelles. But since they have no enzymes with which they can digest their own cargo, they fuse with lysosomes. When a Yoshinori Ohsumi's group in Japan reported that they had discovered ubiquitin-like proteins (ATG8) on the outer surface of the autophagosome and gone on to prove that they were specific for autophagy, Dikic and his colleague Dr. Vladimir Kirkin immediately began their search for potential autophagy receptors that might bind to the family of ATG8 proteins.
The team of international scientists report in the current issue of the renowned journal "Molecular Cell", that by employing methods from cell biology, biochemistry and mouse genetics, they have been able to identify a further protein, in addition to the known p62/SQSTM1 protein, that may act as a receptor. This is the protein NBR1, which has long been associated with cancer. Both proteins have a similar chain-like structure. At one end they bind to the ubiquitin that marks the protein aggregates and organelles that are to be degraded. Next to the ubiquitin-binding site is a domain that binds to the ATG8 proteins found at the autophagosomal membrane. Here, the protein waste can dock onto the autophagosome and can then be wrapped up in the membrane.
Vladimir Kirkin, who is now at Merck Serono in Darmstadt, is continuing these investigations with the long-term aim of developing new drugs. Dikic and his group are now concentrating on mitochondria - which are implicated in oxidative stress in cells - hoping to locate the receptors for autophagy on these important organelles.
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