Nobel Prize in Physiology or Medicine 2013: Vesicle Traffic and the Cell's Transport Machinery

This note covers the Nobel Prize in Physiology or Medicine 2013: who James E. Rothman, Randy W. Schekman and Thomas C.

Südhof are, what problem they solved, how vesicles carry cargo inside our cells, how the discovery unfolded over three decades, why it matters for disease, and quick facts for exams.

What was the Nobel Prize in Physiology or Medicine 2013 awarded for?

The Nobel Assembly at Karolinska Institutet gave the prize to James E. Rothman, Randy W. Schekman and Thomas C. Südhof "for their discoveries of machinery regulating vesicle traffic, a major transport system in our cells".

In plain words, the three laureates worked out how a cell moves its own products from one internal compartment to another, and how it releases some of them to the outside world, at exactly the right place and the right moment.

Cells are not simple bags of chemicals. They are divided into compartments, and molecules such as hormones and chemical messengers have to travel between these compartments in tiny membrane-wrapped parcels called vesicles.

The laureates found the genes and proteins that act like the addressing, docking and release system for this parcel service.

The official name of this award is the Nobel Prize in Physiology or Medicine. The prize was announced on 7 October 2013 and the 2013 prize money was 8,000,000 Swedish kronor, split equally among the three winners.

Who are the laureates?

All three laureates shared the prize equally, each receiving one third, and each had worked on a different piece of the same transport puzzle.

James E. Rothman

James E. Rothman was born on 3 November 1950 in Haverhill, Massachusetts, USA. At the time of the award he was affiliated with Yale University, New Haven, Connecticut, USA, where he was Professor and Chairman in the Department of Cell Biology.

He received a share of one third of the prize. During the 1980s and 1990s, Rothman discovered a protein complex that lets vesicles dock and fuse with the correct target membrane, much like two sides of a zipper locking together.

Randy W. Schekman

Randy W. Schekman was born on 30 December 1948 in St. Paul, Minnesota, USA. At the time of the award he was affiliated with the University of California, Berkeley, California, USA, and with the Howard Hughes Medical Institute, USA.

He received a share of one third of the prize. From the 1970s, using yeast as his experimental organism, Schekman identified a set of genes that are essential for vesicle traffic and sorted them into three functional classes.

Thomas C. Südhof

Thomas C. Südhof was born on 22 December 1955 in Göttingen, Germany. At the time of the award he was affiliated with Stanford University, Stanford, California, USA, and with the Howard Hughes Medical Institute, USA.

He received a share of one third of the prize. Working on nerve cells in the 1990s, Südhof discovered how calcium ions trigger vesicles to release their contents at precisely the right instant.

What problem were the laureates trying to solve?

Every cell in the body behaves a little like a busy factory. It constantly makes molecules such as insulin, digestive enzymes and neurotransmitters (the chemical messengers that let one nerve cell signal another), and it must send each of these products to a precise destination, inside the cell or outside it, at a precise moment.

Scientists already knew, from earlier Nobel-winning work by Albert Claude, George Palade and Christian de Duve on cell structure, and by Günter Blobel on sorting signals in proteins, that the cell is divided into compartments called organelles, and that molecules travel between them packed inside small membrane-covered sacs called vesicles.

What remained a mystery, as the scientific background document for this prize put it, was how these vesicles found their correct destination and how they actually fused with the target membrane to release their cargo.

A cell cannot simply let molecules drift about randomly; wrong delivery would be as damaging as a city's postal service dumping every letter in one street.

The three laureates, working mostly independently and using different organisms and methods, each answered one part of this riddle: how vesicle traffic genes work, how the fusion machinery docks vesicles, and how timing is controlled.

Disturbed vesicle traffic, the Nobel committee noted, lies behind several real diseases, which is why the question was not just a curiosity of cell biology but a medically important one.

How did Schekman find the genes that control vesicle traffic?

Randy Schekman decided to attack the transport problem using genetics rather than chemistry, choosing ordinary baker's yeast, Saccharomyces cerevisiae, because it is genetically easy to study and because it secretes proteins just as human cells do.

He looked for yeast cells whose transport machinery had broken down, which caused vesicles carrying cargo to pile up uselessly inside the cell instead of reaching their destination, a situation the award ceremony speech compared to a poorly planned public transport system where passengers pile up at a station.

His basic method can be summarised as a sequence of steps.

1. Grow yeast cells and look for ones that cannot export proteins properly at a raised temperature, since many such mutations would otherwise be lethal.
2. Identify the yeast cells in which vesicles accumulate abnormally, a sign of a block somewhere in the transport pathway.
3. Pin down which gene is faulty in each defective strain, eventually isolating 23 such genes.
4. Group the genes into three classes, according to whether the traffic jam occurred near the endoplasmic reticulum, the Golgi complex, or at the final step of reaching the cell surface.

This genetic screen gave the field its first list of named components controlling vesicle traffic, and it later turned out that several of Schekman's yeast genes corresponded to the very proteins Rothman was finding independently in mammal cells, showing that this transport machinery is extremely ancient in evolutionary terms.

How did Rothman discover the docking and fusion machinery?

James Rothman took a biochemical route. Working first on mammalian cells, he built a test-tube system that could reconstruct the transport of a viral marker protein through the layers of the Golgi complex, which let him isolate, one by one, the actual proteins needed for vesicles to fuse with their target membrane.

The first protein he purified in this way was a fusion factor, later followed by partner proteins, and eventually by a set of three proteins he named SNAREs (soluble NSF-attachment protein receptors).

Rothman found that one SNARE protein sits on the vesicle and matching SNARE proteins sit on the target membrane, and that they lock together like the two sides of a zipper, so that cargo is delivered only to the correct destination.

Draw a vesicle as a small circle approaching a flat target membrane.

Label a protein sticking out of the vesicle surface as the "v-SNARE" and a matching protein on the target membrane as the "t-SNARE".

Draw the two proteins interlocking like a zipper, and show the vesicle membrane merging with the target membrane once they lock together, releasing the cargo inside.

How did Südhof explain the timing of vesicle release?

Rothman and Schekman had worked out the basic fusion machinery, but something else was needed to explain why a vesicle does not fuse and release its cargo all the time.

Nerve cells, in particular, must release their neurotransmitter-filled vesicles only in a tiny fraction of a second, exactly when a nerve signal arrives.

Thomas Südhof studied nerve cells and found that this precise timing is controlled by calcium ions.

He identified proteins, including one called synaptotagmin, that sense a sudden rise in calcium inside the nerve terminal and respond by rapidly pulling the vesicle and target membrane together so the zipper-like SNARE proteins can finish the fusion and release the neurotransmitter.

He also studied a related protein that normally holds the system back, acting as a brake that is released only at the right moment.

Draw a nerve terminal with several vesicles waiting near the membrane. Show a nerve signal arriving and calcium ions (Ca²⁺) flowing in through a channel.

Draw an arrow from the calcium ions to a sensor protein on the vesicle, and then show the vesicle fusing with the membrane and releasing neurotransmitter dots into the gap between two nerve cells.

Together, the three discoveries build a complete picture: Schekman's genes supply the basic machinery, Rothman's SNARE proteins provide the docking and fusion step, and Südhof's calcium sensors provide the switch that decides exactly when fusion happens.

The Nobel Assembly said the laureates had "revealed the exquisitely precise control system for the transport and delivery of cellular cargo".

How did the discovery unfold?

Why does this discovery matter?

Vesicle transport is not a side detail of cell biology; it underlies many of the body's most basic signalling and secretion processes. The Nobel Assembly said that without this precise organisation, "the cell would lapse into chaos".

Nerve signalling in the brain, the release of hormones such as insulin, and the sending out of immune signalling molecules called cytokines all depend on vesicles fusing correctly and at the right time.

Because the same machinery is used throughout the body, faults in it are linked to a range of diseases. The scientific background document names disturbances in vesicle traffic as contributing to neurological diseases, diabetes and immunological disorders.

Specific gene faults in this machinery have also been linked to certain forms of epilepsy and to a severe immune condition called Familial Hemophagocytic Lymphohistiocytosis, in which immune cells fail to control their release of harmful substances.

The same system is also the target of dangerous bacterial toxins: the toxins that cause botulism and tetanus both work by cutting up SNARE-type proteins, which is why they cause paralysis.

By mapping this shared machinery across organisms as different as yeast and humans, the three laureates gave later researchers a common language and a set of named proteins to study when investigating these diseases, even though the prize work itself was basic cell biology rather than a direct treatment.

How does this connect to what you study?

School biology usually introduces the cell as having a nucleus, a cell membrane and organelles such as the endoplasmic reticulum and Golgi apparatus, often taught together under cell structure and secretion.

This prize puts flesh on that picture by explaining how molecules actually move between those organelles and leave the cell: packed into vesicles that bud off one membrane and fuse with another.

It also connects to lessons on the nervous system and hormones. The release of a neurotransmitter at a nerve synapse, or the release of insulin from the pancreas into the blood, are both examples of the same type of vesicle fusion process that the three laureates' work explained.

Understanding this molecular "postal system" gives a concrete mechanism behind processes that are often described only at the level of "a signal is released" in introductory biology.

Quick facts for exams

The Nobel Prize in Physiology or Medicine 2013 was awarded jointly to James E. Rothman, Randy W. Schekman and Thomas C. Südhof "for their discoveries of machinery regulating vesicle traffic, a major transport system in our cells".

It was announced on 7 October 2013 by the Nobel Assembly at Karolinska Institutet, which awards this prize. Each laureate received an equal one-third share of the 8,000,000 Swedish kronor prize.

Rothman and Schekman were both born in the United States, while Südhof was born in Germany; at the time of the award, Rothman worked at Yale University, Schekman at the University of California, Berkeley, and Südhof at Stanford University.

Their combined work explained how cells transport and deliver molecular cargo using vesicles, with Schekman supplying the genetics, Rothman the docking machinery and Südhof the timing mechanism.

Note: Source. The prize facts in this note are from the Nobel Prize's official site, nobelprize.org.

Glossary

• Vesicle — a tiny sac wrapped in its own membrane, used inside a cell to carry molecules from one place to another.
• Organelle — a distinct compartment inside a cell, such as the Golgi complex, that carries out a specific job.
• Endoplasmic reticulum (ER) — the organelle where many proteins destined for secretion are first produced.
• Golgi complex — an organelle that processes and sorts proteins after they leave the endoplasmic reticulum.
• SNARE protein — one of a family of proteins, found on both vesicles and target membranes, that lock together to drive membrane fusion.
• Synaptotagmin — a calcium-sensing protein identified by Südhof that helps trigger rapid vesicle fusion at nerve endings.
• Neurotransmitter — a chemical messenger released by one nerve cell that signals to a neighbouring nerve cell.
• Yeast genetics — the study of genes using yeast, a simple single-celled organism that is easy to grow and mutate in the laboratory.
• Calcium ion (Ca²⁺) — a charged particle whose sudden rise inside a nerve terminal signals vesicles to release their contents.
• Exocytosis — the process by which a vesicle fuses with the outer cell membrane and releases its contents outside the cell.
• Temperature-sensitive mutant — a yeast strain carrying a gene fault that only breaks down at a raised temperature, used by Schekman to study otherwise lethal genes.
• Botulism — a paralytic disease caused by a bacterial toxin that cuts up SNARE proteins, blocking nerve signal release.

Common errors and misconceptions

• Misconception: The three laureates worked as one team on one experiment. Correct: They worked largely independently, in different laboratories and organisms, though Rothman and Schekman did collaborate directly on cloning one gene, and most of their findings only later turned out to fit together.
• Misconception: The prize is only about yeast biology. Correct: Schekman used yeast genetics, but Rothman worked on mammalian cells and Südhof worked on nerve cells from mice.
• Misconception: Vesicles are only involved in nerve signalling. Correct: Vesicle traffic also carries out hormone secretion, such as insulin release, and immune signalling.
• Misconception: SNARE proteins were discovered by Südhof. Correct: SNARE proteins were identified and named by James Rothman's group.
• Misconception: The prize money was shared unequally based on who contributed more. Correct: All three laureates received an equal one-third share.
• Misconception: This discovery directly produced a new medicine. Correct: The work was basic cell biology; the sources describe it as explaining disease mechanisms, not as producing a treatment itself.
• Misconception: Vesicle fusion machinery is unique to humans. Correct: The sources state that it operates on the same general principles in organisms as different as yeast and humans.

Exam-style questions with model answers

Q1. In which year was the Nobel Prize in Physiology or Medicine 2013 announced? [1 mark]

1. It was announced on 7 October 2013.

Q2. Name the three laureates of the Nobel Prize in Physiology or Medicine 2013. [2 marks]

1. The laureates were James E. Rothman, Randy W. Schekman and Thomas C. Südhof, who shared the prize equally for their work on vesicle traffic.

Q3. State the official citation for the Nobel Prize in Physiology or Medicine 2013. [2 marks]

1. The citation reads "for their discoveries of machinery regulating vesicle traffic, a major transport system in our cells".

Q4. Explain how Randy Schekman's experiments revealed genes controlling vesicle traffic. [4 marks]

1. Schekman worked with baker's yeast because it is genetically easy to study and secretes proteins like human cells do.
2. He used temperature-sensitive mutants so that genes that would otherwise be lethal could still be studied.
3. He looked for yeast cells in which vesicles piled up abnormally, a sign that transport was blocked.
4. By identifying the faulty genes in these mutants, he found 23 genes, which he grouped into three classes controlling different stages of the transport pathway.

Q5. Describe the role of SNARE proteins discovered by James Rothman. [4 marks]

1. Rothman found that vesicles carry one type of SNARE protein and target membranes carry a matching partner SNARE protein.
2. These proteins bind to each other like the two sides of a zipper, locking the vesicle onto the correct target.
3. Because each SNARE pairs only with certain partners, cargo is delivered specifically to the right location rather than at random.
4. This zipper-like docking was found to operate both inside the cell and when a vesicle fuses with the outer cell membrane.

Q6. Discuss how the discoveries of Rothman, Schekman and Südhof together explain vesicle transport, and why disturbances in this system matter for medicine. [6 marks]

1. Schekman's yeast genetics identified the genes essential for vesicle traffic and sorted them into classes governing different stages of transport.
2. Rothman's biochemical work found the SNARE proteins that let vesicles dock and fuse specifically with their correct target membrane, like a zipper.
3. Südhof discovered that calcium ions trigger a sensor protein which controls exactly when a vesicle is allowed to fuse and release its cargo.
4. Together these three contributions explain how cargo such as neurotransmitters and hormones is delivered with both precision of location and precision of timing.
5. Because the same machinery operates throughout the body, faults in it are linked to neurological diseases, diabetes and immunological disorders.
6. Certain bacterial toxins, such as those causing botulism and tetanus, also act by damaging this same SNARE machinery, which explains their paralytic effects.

Key takeaways

• The Nobel Prize in Physiology or Medicine 2013 went jointly to Rothman, Schekman and Südhof for discovering how vesicle traffic is regulated in cells.
• Vesicles are tiny membrane-wrapped sacs that carry molecules between compartments inside a cell or release them outside it.
• Schekman used yeast genetics to identify genes essential for vesicle transport, sorted into three functional classes.
• Rothman discovered the SNARE proteins, which let vesicles dock and fuse with the correct target membrane like a zipper.
• Südhof discovered that calcium ions trigger the precise timing of vesicle fusion, especially at nerve endings.
• The three laureates' work together shows that this transport machinery is shared across organisms as different as yeast and humans.
• Faults in this machinery are linked to neurological disease, diabetes and immune disorders, and are exploited by bacterial toxins such as those causing botulism.
• Each laureate received an equal one-third share of the 8,000,000 Swedish kronor prize, announced on 7 October 2013.

Test yourself

Where was James E. Rothman affiliated at the time of the award?

James E. Rothman was affiliated with Yale University in New Haven, Connecticut, USA, at the time of the 2013 award.

Which organism did Randy Schekman use to study vesicle traffic genetically?

Randy Schekman used baker's yeast, Saccharomyces cerevisiae, because it is genetically easy to study and secretes proteins like human cells.

What did James Rothman name the proteins that let vesicles dock with target membranes?

Rothman named these proteins SNAREs, which stands for soluble NSF-attachment protein receptors, and they bind like two sides of a zipper.

What ion did Südhof find controls the precise timing of vesicle fusion?

Südhof found that calcium ions trigger sensor proteins, such as synaptotagmin, which control exactly when a vesicle releases its contents.

Where was Thomas Südhof born?

Thomas Südhof was born on 22 December 1955 in Göttingen, Germany.

Name two diseases linked by the sources to faults in vesicle transport machinery.

The sources link faults in this machinery to conditions including neurological diseases, diabetes and immunological disorders such as certain immune cell disorders.

How much was the total Nobel Prize money for the 2013 Physiology or Medicine prize?

The 2013 Nobel Prize in Physiology or Medicine carried a total prize amount of 8,000,000 Swedish kronor, shared equally among the three laureates.