Monday, May 21, 2007

1st Draft of Hartwell_Avram_Huber's work

Leland H. Hartwell
The Nobel Prize in Physiology or Medicine 2001
Leland Hartwell won the 2001 Nobel Prize for Physiology orMedicine, together with Tim Hunt (2002, Protein synthesis, proteolysis, and cell cycle transitions. Biosci.Rep. 22:465–486) and (Sir) Paul M Nurse (2002, Cyclin dependent kinases and cell cycle control. Biosci. Rep. 22:487–499). The prize was awarded to the three scientists for their discoveries of key regulators of the cell cycle.
Why yeast?
The motivation of Hartwell’s research career was to understand cancer. He found that intriguing aspect of cancer problems can be resolved by studying a simple eukaryotic cell, Saccharomyces cerevisiae, than the human cell. One reason for this is that it is relatively easy to obtain mutants, and then to characterize them, in yeast. And mutants that fail to carry out important controlling functions in cell growth have been key to Hartwell’s approach. Also the cancer cells grew in plastic Petri dishes when normal cells did not.
Yeast model to cancer research
Hartwell et al. studied the fidelity of chromosome transmission in yeast cells to learn more about how chromosome fidelity is maintained in the normal cell cycle. The genetic instability of cancer cells is due to genetic defects that affect the cell cycle machinery, DNA repair, or cell cycle checkpoints. Since the biochemistry of each of these processes are well known, it was possible to define the genetic changes that lead to loss of fidelity in many cancers. These defects created a vulnerability for the cancer cell relative to the normal cell that provided a powerful therapeutic advantage if the appropriate vulnerability were targeted for therapeutic intervention. So, a drug discovery program was developed to understand yeast genetics to discover and validate cancer targets. The goal was to identify drugs and drug targets that would present a therapeutic advantage. That is, where the cancer cells would be more sensitive to the drug or to inhibition of the target than the normal cells. The idea was to construct yeast cells that contained mutations characteristic of specific tumors (altered in mismatch repair, cyclin, activated telomerase, etc.). The mutant and normal cells were screened for drugs that killed the mutant yeast more effectively than wild-type yeast. This approach identified drugs with therapeutic advantage. In addition, the protein targets were identified which if inhibited by drugs would provide therapeutic advantage. Yeast lends itself to this goal. So, a mutation characteristic of certain types of cancer was studied and mutations in few genes were identified. These genes were the potential drug targets. Targets were identified that would kill mutants defective in the DNA damage checkpoint. These targets were enzymes of deoxynucleotide biosynthesis and components of the DNA replication apparatus.
1. Hartwell, L. H., (2004), Yeast and Cancer. Bioscience Reports, 24 (4/5): 525- 544.
2. Hartwell, L. H., Szankasi, P., Roberts, C. J., Murray, A. W., and Friend, S. H. (1997) Integrating genetic approaches into the discovery of anti-cancer drugs. Science 278:1064–1068.
3. Bender, A. and Pringle, J. R. (1991) Use of a screen for synthetic lethal and multicopy suppresser mutants to identify two new genes involved in morphogenesis in Saccharomyces cerevisiae. Mol. Cell Biol. 11:1295–1305.
Hershko, Avram
The Nobel Prize in Chemistry 2004
Avram Hershko won the Nobel Prize with Aaron Ciechanover, and Irwin Rose, to contribute on the ground-breaking chemical knowledge of how the cell can regulate the presence of a certain protein by marking unwanted proteins with a label consisting of the polypeptide ubiquitin. Proteins so labelled are then broken down, degraded rapidly in cellular "waste disposers" called proteasomes. This discovery helped them to demonstrate the ubiquitin-mediated protein degradation that helps controlling a number of other critical biochemical processes, including cell division, the repair of defects in DNA, and gene transcription, the process in which genes use their coded instructions to manufacture a protein. Diseases such as cystic fibrosis result when the protein-degradation system does not work normally, and researchers hoped to use the findings to develop drugs for the treatment of such illnesses.
Avram Hershko studied reticulocyte extract that contained large quantities of haemoglobin. In the attempts to remove the haemoglobin using chromatography, Aaron Ciechanover and Avram Hershko discovered that the extract could be divided into two fractions, each inactive on its own. But it turned out that as soon as the two fractions were recombined, the ATP-dependent protein degradation restarted. In 1978 the researchers reported that the active component of one fraction was a heat-stable polypeptide with a molecular weight of only 9000 which they termed APF-1 (active principle in fraction 1). This protein later proved to be ubiquitin. It was shown that APF-1 was bound covalently, i.e. with a very stable chemical bond, to various proteins in the extract. It was further shown that many APF-1 molecules could be bound to the same target protein; the latter phenomenon was termed polyubiquitination. Polyubiquitination of substrate proteins is the triggering signal that leads to degradation of the protein in the proteasome. It is this reaction that constitutes the actual labelling, the "kiss of death" if you will.
Since ubiquitin occurs so generally in various tissues and organisms, ubiquitin-mediated protein degradation are of general significance for the cell. The ubiquitin system has become an interesting area of research for medicines against various diseases. Such preparations can be aimed at components of the ubiquitin-mediated breakdown system to prevent the degradation of specific proteins. They can also be designed to cause the system to destroy unwanted proteins. A medicine already being tested clinically is the proteasome inhibitor Velcade (PS341) which is used against multiple myeloma, a cancer disease that affects the body's antigen-producing cells.

Robert Huber
The Nobel Prize in Chemistry 1988

Robert Huber received the Nobel Prize jointly with Johann Deisenhofer and Hartmut Michel. The trio was recognized for their work in first crystallizing an intramembrane protein important in photosynthesis in cyanobacteria, and subsequently applying X-ray crystallography to quantify the protein's structure. The information provided the first insight into the structural bodies that performed the integral function of photosynthesis. This insight could be translated to understand the more complex analogue of photosynthesis in plants.

Huber began his work with studies of proteins involved in excitation energy and electron transfer, light-harvesting proteins, later bili-building protein, the reaction centre and in ascorbate oxidase. His work has led to the development of methods on protein crystallography and the elucidation of protein structures which serve as targets for ligand design and development in medicine and plant protection including the key components of photosynthesis. It has also led to the development of Patterson search methods, to methods and suites of computer programmes to identify data evaluation and absorption of correction, for protein crystallographic computing, for computer graphics and electron density interpretation and refinement and for area detector data collection. These methods and programmes are in use in many laboratories in the world today.
A protein was taken from a photosynthetic bacterium which, like green plants and algae, uses light energy from the sun to build organic substances. The organic substances serve as nourishment for both plants and animals. Using the oxygen in the air, plants and animals consume these nutrients through what is termed cellular respiration. The conversion of energy in photosynthesis and cellular respiration takes place through transport of electrons via a series of proteins, which are bound in special membranes. These membrane-bound proteins are difficult to obtain in a crystalline form that makes it possible to determine their structure, but in 1982 Hartmut Michel succeeded in doing this. Determination of the structure was then carried out in collaboration with Johann Deisenhofer and Robert Huber between 1982 and 1985.
Photosynthesis in bacteria is simpler than in algae and higher plants, but the work rewarded in 1988 led to increase understanding of photosynthesis in these organisms as well. Broader insights have also been achieved into the problem how electrons can, at an enormously high speed (in a billionth of a second), be transferred in biological systems.

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