Dr. Maya Shuldiner and the members of her group in the Department of Molecular Genetics of the Weizmann Institute of Science, decided to look for pairs of proteins: a protein that needs transport to take it out of one of the cell organelles, and a chaperone protein that helps it reach its transport
It is not easy to arrange a pile of thousands of socks in pairs. The problem gets really complicated when it turns out that they are microscopic socks. This task is beginning to approach the challenge faced by Dr. Maya Shuldiner and her group members in the Department of Molecular Genetics of the Weizmann Institute of Science, when they decided to look for pairs of proteins: a protein that needs transport to take it out of one of the cell organelles, and a chaperone protein that helps it reach its destination. Dr. Shuldiner and my friends Her group had to adapt the robotic equipment in the lab to develop a system called PAIRS, which prepares Thousands of examples and looking for suitable pairs among them.
Many scientists have been trying to find such pairs for two decades, with only partial success. This is a matter of the utmost importance: the accompanying proteins bind to hormones, growth factors, and other signaling molecules, which are formed in the cell and need to leave it to other cells or organs, and are involved in many diseases, from autoimmune diseases to cancer. A better understanding of the accompanying proteins may indicate targets for drugs to treat these diseases.
The first stop on the journey of all proteins that need to leave the cell, as well as proteins that are eventually displayed on the outer surface of the cell membrane, is the intraplasmic reticulum - a labyrinth-like organelle formed from folded inner membranes. The proteins that enter the intra-plasmic reticulum fold inside it into their final form, and undergo a quality check before exiting the labyrinth. The exit towards the next station - the Golgi - for the purpose of sorting and final routing, is a more complicated move than the entrance. The protein, which is now folded and in an active state, must travel inside a small bubble of membrane that separates from the intraplasmic reticulum and forms a vesicle - a sort of private taxi that brings the passenger to the Golgi without contact with the inside of the cell. At this point, the lenders also enter the picture. They sort and package the proteins, and make sure that only the prepared proteins leave the intraplasmic reticulum, and that they enter the appropriate vesicles.
Until now, the attempt has been made to match the proteins and their attendants in a similar way to matching socks by manual sorting - that is, one by one. In this way, only ten attendants have been identified to date, and only a number of spouses have been found for these. According to Dr. Schuldiner, this information is not enough to even begin to understand the laws of movement of proteins.
Dr. Shuldiner and the members of her team, which included research student Yonatan Herzig and Dr. Yael Elbaz, as well as colleagues from the University of Cambridge, believed that a more systematic and orderly approach was needed. In the PAIRS method they developed, they used a robot that prepared cultures of yeast cells. Each of the samples contained a genetically modified yeast strain, one of the 400 different proteins found in it was colored a glowing green. In addition, one of the ten known companions has been engineered to be inactive. A total of 4,000 different samples were produced, the purpose of which was to find the spouses of the familiar companions. Another robot automatically scanned photographs of the cells, looking for proteins painted in glowing green that gathered inside the cell instead of leaving it - which was a sign of a match between the green protein and an inactive chaperone.
The team found new passenger proteins for each known chaperone. This was enough, according to Dr. Schuldiner, to begin deciphering some of the basic rules of the movement system in the intraplasmic retina. Thus, for example, the scientists discovered that most chaperones work with small groups of proteins, and that each protein uses only one type of chaperone. In some cases, the group of proteins that used one chaperone had a similar function. In other cases, a common chemical "password" linked several proteins to one particular chaperone In the journal PLos Biology.
The most interesting of all was an accompanying protein that apparently exhibited exceptional behavior: the scientists noticed that Erv14 connects to a large amount of proteins, which at first glance did not have any connection between them. After a long series of experiments in which several possible explanations were ruled out, the scientists finally discovered the common denominator: it turns out that all the proteins that use Erv14 need a particularly long sequence of amino acids to protrude from the cell's outer membrane.
Different versions of the chaperone Erv14 are found in all living things, from yeast and fruit flies to humans, and therefore, it is likely that the findings are also valid for the human chaperone and the proteins that use it. One of those proteins is the receptor for the growth factor EGF, a protein necessary for normal fetal development, which also plays a role in cancer. A better understanding of the movement of the EGF receptor is important for the development of models that describe the development and progression of cancerous tumors.
In addition to the pairs that the scientists were able to identify, many proteins were also found that did not connect to any known chaperones. Do these proteins manage on their own, unaccompanied, or perhaps they use other chaperones, which have not yet been identified? Dr. Schuldiner and her team members intend to continue researching the issue. Their future goal is to create a database that maps the transport systems of all proteins in the cell.
