The story of Fred Sanger

How is it the saying goes? From little potatoes, big Nobel Prizes grow? Well, maybe not exactly that. But the story of Fred Sanger illustrates perfectly how - as so often in science, and, indeed, in life - inauspicious beginnings lead to stunning results.

Fred Sanger, the son of a Cotswolds GP and sometime missionary, started off studying physics with chemistry at Cambridge. It wasn’t the most brilliant start: he decided to give up the physics because he struggled with the maths. However, he excelled in chemistry and chose to do further studies in biochemistry. As a Quaker, he was a conscientious objector (COs) during the Second World War and was granted full exemption from military service by a tribunal. History tells us that COs were often subjected to ridicule and accused of disloyalty. Many COs contemplated going to war against their principles as their experiences of staying home were so negative. But stay, Fred Sanger did, and it was during the war years that he gained his PhD. After his first supervisor left the department, Sanger chose a new project, studying the amino acid lysine. His first paper was on the glamorous topic of the nitrogen uptake of the potato.

Proteins piqued Sanger’s interest, and joining the research group of Charles Chibnall, a protein chemist, he was encouraged to study insulin. Sanger credited Chibnall for the successful direction his career took, saying in an interview in 2007, “without him I would have continued metabolic work which would not have come to much.” Insulin seemed like a good protein to study, as in bovine form, it was available in plentiful supply from Boots (the chemist) and of course, it was medically important. However, his initial application for a grant from the Medical Research Council to study its structure was rejected, as at the time, everyone thought the pattern of amino acids in a protein was simply random.

Sanger had the last laugh, though: Working in an outbuilding he termed ‘the protein hut,’ he developed a reagent (now known as Sanger’s reagent) which identified the N-terminals of the amino groups. In doing so, he was able to show that insulin was composed of two polypeptide chains and identify the amino acids at the ends. He then used a partition chromatography method to determine the precise amino acid sequence of bovine insulin A and B in 1951 and 1952 respectively. From this discovery, he was able to conclude that by extension, every protein had a unique sequence. It was this discovery which won him the Nobel Prize for Chemistry in 1958.

The Medical Research Council, previously dismissive of his efforts, now welcomed him as the head of the protein chemistry division at their molecular biology lab in Cambridge. He started working on nucleic acids, first of all RNA. Sanger said of that time that he was lucky not to be under time pressure to produce papers as the progress was very slow. Going from sequencing proteins, a few hundred amino acids long, to much longer nucleic acids required another change in technology. But the hard work and time paid off, and by 1967, the group had sequenced the 5S ribosomal RNA structure of E. Coli. Perhaps to our modern ears, the structure of a small 120-nucleotide RNA from a bacterium most commonly heard about in food hygiene scares doesn’t sound like much, but here’s where the story really gets exciting.

Sanger, realising its importance, turned his team’s attention to sequencing DNA. Pure DNA was hard to come by but they were able to extract it from phages (viruses within bacteria). However, DNA was a dauntingly large structure, even that from the tiniest microorganism. To tackle it, Sanger knew he had to break it down. Still in the protein hut, he developed a method he called the ‘plus and minus’ method for DNA sequencing, whereby short oligonucleotides with defined 3’ termini were generated, electrophoresed and then visualised by autoradiography. This laborious process, which could sequence up to 80 nucleotides at a time, led to the first fully-sequenced DNA-based genome, that of the single-stranded bacteriophage; ϕX174.

The ‘plus and minus’ method was okay. Arduous, maybe, but nonetheless faster than its predecessors. But it had a few problems, not least of which that it could only be used for single-stranded DNA. So Sanger’s team chipped away, trying to find a better, quicker way to accurately sequence DNA. And find it they did, in 1977, in the dideoxy chain-termination method. This was based on the finding that dideoxynucleotides could inhibit chain elongation. Since dideoxynucleotides (ddGTP, ddATP, ddTTP and ddCTP) do not contain a 3’ hydroxyl group, when they were incorporated into a DNA chain in place of their corresponding deoxynucleotide (G, A, T C), no new phosphodiester bonds could be created and the growing DNA chain was terminated. So by adding a small amount of chain terminators (much less than the corresponding base) to the DNA replication mixture, Sanger’s team were able to obtain a mixture of DNA fragments of varying sizes, all with the same deoxynucleotide residues at their 3’ ends. By using corresponding terminators for each nucleotide in turn, and then electrophoresing the four different reactions in parallel, the DNA sequence could be obtained. They used this new method to sequence human mitochondrial DNA.

Of course, the dideoxy chain-termination method is what now goes by the far snappier title of Sanger sequencing. And it was this that, in 1980, secured Fred Sanger’s membership into the select group of just four individuals who have won a Nobel Prize more than once. To date, he is the only person to have won it twice for chemistry. As well as being awarded many other honours, he also supervised more than ten PhD students in his working lifetime, two of whom went on to win Nobel Prizes of their own.

Today, Sanger’s name is synonymous with DNA sequencing. It was Sanger sequencing which led to the eventual sequencing of the entire human genome in 2003. Yet throughout his career and beyond, Sanger was known for his humility. “Unlike most of my scientific colleagues,” he wrote in a 1988 article, “I was not academically brilliant.”

Source:- https://www.futurelearn.com/courses/molecular-techniques/6/steps/765681