An Israeli researcher discovered the "smart zone" in proteins involved in diseases such as cancer and diabetes. Blocking the region may contribute to the development of drugs for these diseases
05/06/2002
By Marit Selvin
The enrichment of biological knowledge following the human genome project led, among other things, to a more sophisticated development of medicines. The exact structure of thousands of proteins is now known, and it poses new challenges: the development of new materials, based on understanding the structure of proteins. The drugs of the next generation will directly hit the target by blocking the activity of key proteins that disrupt the biochemical processes and thus cause the development of diseases.
An important step in this direction was taken at the Hebrew University by a team of researchers led by Prof. Shmuel Ben Sasson, from the Department of Experimental Medicine and Cancer Research. Prof. Ben Sasson was able to locate a unique region in protein molecules that regulates key processes in the cell. His discoveries allow the development of drugs that have the potential to treat a wide variety of serious diseases - cancer, diabetes, acute inflammatory reactions and more.
This work earned Ben Sassoon first place in the Kay Prize competition for innovative developments on behalf of the Hebrew University, which will be awarded to him today.
"It all started by chance, when I was on sabbatical in the US," says Ben Sassoon. "I tested a short peptide (protein segment) four amino acids long, which inhibited cell division. I suspected that the peptide I tested mimicked in its structure an active site of a protein that participates in cell division, and as happens in many cases of inhibiting biological processes, I hypothesized that the peptide binds to the active site and succeeds in blocking the activity of the protein and thereby inhibiting division. To know who this protein is, I looked for proteins that contain the sequence of that short peptide. It became clear to me that proteins containing this sequence belong to a large family of enzymes called protein kinases and participate in signal transmission processes in the cell."
Almost all key processes in the cell are mediated by a chain of signals transmitted from protein to protein. The protein kinases participate in signal transduction by binding a phosphorus molecule to their target protein. The small chemical change causes the phosphorylated protein to switch from an "off" state to an active state, just like an electrical switch that opens and closes. In certain cancers, a "short" occurs in the transmission of signals, resulting in a constant signal - like a bell that is caught and rings all the time. The constant activation of the signals leads to an uncontrolled division of the cell. Increased signaling is also present in diseases related to the immune system, leading to severe and prolonged inflammatory responses.
Ben Sassoon decided to check if the peptide he had was indeed capable of inhibiting the protein kinases. He added three amino acids to the existing four amino acids, and when he added the new seven-amino acid peptide to cell culture, the inhibition of cell division increased a thousandfold.
"There are about a thousand different protein kinases in the human body, and they are all built according to a more or less fixed model," says Ben Sasson. "They contain 300-200 amino acids, their three-dimensional structure is remarkably similar and they perform the same activity - protein phosphorylation." A careful analysis of the structure and function of the region from which the peptide Ben Sasson tested was derived showed that it is the "strategic" region of the kinase: in this region there is a consistent difference between different protein kinases. "I thought that this is probably the site that determines the uniqueness of the kinase and is responsible for a certain protein in the chain being phosphorylated by one kinase and not another," says Ben Sassoon.
"You can compare it to different people's credit cards," he continues. "All credit cards are similar to each other in their external contours, but they all have a 'smart' area - the magnetic strip - where the uniqueness of the card holder is determined; and if someone wants to defraud the system, he will refer only to this section. The same is true of kinases. If we know where Once this uniqueness is determined, we will be able to create short peptides that mimic the structure of this 'smart' region and inhibit the transmission of signals in disease states."
Ben Sassoon had at his disposal a database that provided him with hundreds of structures of protein kinases whose amino acid sequence is known. "We arranged the kinases in rows, like soldiers, and looked for a region within the general sequence where the sequence differs from one kinase to another. This is the region responsible for the fact that each kinase can only bind to its target protein," says Ben Sasson. The team also discovered that in protein kinases that play similar roles, in different animals, the sequence of amino acids in this region was similar, while in protein kinases that play different roles in the same animal, the sequence was completely different. "This is what we would expect from a region that determines the uniqueness of protein kinases," says Ben Sassoon.
After doing additional tests to verify the findings, Ben Sassoon says, "Everything suddenly came together for me, and it gave me the courage to generalize and say: 'I identified the location of the target protein link in the active site of the protein kinase family as a whole.' The applied potential of the findings was clear: substances that blocked this site could be used as a basis for drugs in cases where the protein kinase is activated in an abnormal way and causes diseases. Ben Sasson registered a patent for his findings and in 1997 a start-up was established in cooperation with the "Yishom" company of the Hebrew University. From the start-up, the company "Crix" was established, which develops unique inhibitors for kinases involved in disease states.
Inhibitors of this type are supposed to uniquely damage the processes that lead to the development of cancer and other serious diseases. Ben Sassoon and his research group discovered that one of the kinases they tested is involved in the development of prostate cancer, and that its inhibition results in tumor inhibition. The company is developing substances that will block the active site in this kinase and in a variety of protein kinases involved in other diseases.
The work begins with bioinformatics people who identify the active region and use the computer to design similar molecules that can mimic this region. The laboratory personnel then synthesize these molecules and test in vitro and in tissue cultures whether they inhibit cell activity. The computer people analyze the results and try to prepare a second, improved generation of materials, until the desired result is obtained. Today, Crix possesses a substance that inhibits the development of prostate cancer. Its effectiveness has been tested in laboratory mice and tissue cultures, and pre-clinical trials will soon begin with the aim of treating humans. Other projects that are in the development stages include drugs for diabetes and to prevent acute inflammatory reactions.
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