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         Dr Yoshinori Ohsumi was awarded the Nobel Prize for Physiology or Medicine in 2016 for his pioneering work on how cells recycle their content.
respect during modern times in the West, under the new term of intermittent fast- ing, which has found place in the diction- ary of health science.
YOSHINORI OHSUMI’S WORK
The 2016 Nobel laureate discovered mechanisms underlying autophagy, a fundamental process for degrading and recycling cellular components. Au- tophagy denotes ‘self-eating’. This con- cept emerged during the 1960s, when researchers first observed that the cell could destroy its own contents by enclos- ing it in membranes, forming sack like vesicles that are transported to a recy- cling compartment, called the lysosome, for degradation. Difficulties in studying the phenomenon were removed through a series of brilliant experiments in the early 1990s by Yoshinori Ohsumi that led to a new paradigm in our understanding of how the cell recycles its content. His dis- coveries opened the path to understand- ing the fundamental importance of au- tophagy in many physiological processes, such as in the adaptation to starvation or response to infection. Mutations in au- tophagy genes can cause disease, and the autophagic process is involved in several conditions including cancer and neuro- logical disease.
DEGRADATION: A CENTRAL FUNCTION IN ALL LIVING CELLS
In the mid-1950s, scientists observed a new specialised cellular compartment containing enzymes that digest proteins, carbohydrates and lipids. This specialised compartment is referred to as ‘lysosome’ and functions as a workstation for deg- radation of cellular constituents.
The Belgian scientist Christian de Duve was awarded the Nobel Prize in Physiol- ogy or Medicine in 1974 for the discovery of the lysosome. New observations dur- ing the 1960s showed that large amounts of cellular content, and even whole or- ganelles could sometimes be found inside lysosomes. The cell therefore appeared to have a strategy for delivering large cargo to the lysosome. Further biochemical and microscopic analysis revealed a new type of vesicle transporting cellular cargo to the lysosome for degradation. Christian De Duve coined the term ‘autophagy’ to
Ohsumi elucidated that during fasting, autophagy is activated, which slows down the aging process, improves immunity and also helps in weight loss.
describe this process. The new vesicles were named autophagosomes.
During the 1970s and 1980s, re- searchers focused on elucidating another system used to degrade proteins, namely the ‘proteasome’. Aaron Ciechanover, Avram Hershko and Irwin Rose were awarded the 2004 Nobel Prize in Chem- istry for “the discovery of ubiquitin- me- diated protein degradation”.
The proteasome efficiently degrades proteins one-by-one, but this mechanism did not explain how the cell got rid of larger protein complexes and worn-out organelles. Could the process of autoph- agy be the answer and, if so, what were the mechanisms?
A GROUNDBREAKING EXPERIMENT
Yoshinori Ohsumi had been active in various research areas, but upon starting his own lab in 1988, he identified the first genes essential for autophagy. The results showed that autophagy is controlled by a cascade of proteins and protein com- plexes, each regulating a distinct stage of autophagosome initiation and forma- tion. This was a major breakthrough and Ohsumi published the results in 1992. Carbohydrates are broken down into individual glucose (sugar) units, which can be linked into long chains to form
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        Image Courtesy: nytimes.com




















































































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