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Born on this day
Frederick Sanger
Frederick Sanger is a British biochemist and a Nobel Prize winner.
33rd week in year
13 August 2019

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Frederick Sanger13.8.1918

Wikipedia (30 Jul 2013, 12:08)

Frederick Sanger, (born 13 August 1918, Rendcomb) is a British biochemist who was twice the recipient of the Nobel Prize for Chemistry, the only person to have been so. In 1958 he was awarded a Nobel prize in chemistry "for his work on the structure of proteins, especially that of insulin". In 1980, Walter Gilbert and Sanger shared half of the chemistry prize "for their contributions concerning the determination of base sequences in nucleic acids". The other half was awarded to Paul Berg "for his fundamental studies of the biochemistry of nucleic acids, with particular regard to recombinant-DNA".

He is the fourth person to have been awarded two Nobel Prizes, either individually or in tandem with others.

Sequencing insulin

Neuberger moved to the National Institute for Medical Research in London but Sanger stayed in Cambridge and in 1943 joined the group of Charles Chibnall, a protein chemist who had recently taken up the chair in the Department of Biochemistry. Chibnall had already done some work on the amino acid composition of bovine insulin and suggested that Sanger look at the amino groups in the protein. Insulin could be purchased from Boots and was one of the very few proteins that were available in a pure form. Up to this time Sanger had been funding himself. In Chibnall's group he was initially supported by the Medical Research Council and then from 1944 until 1951 by a Beit Memorial Fellowship for Medical Research.

Sanger's first triumph was to determine the complete amino acid sequence of the two polypeptide chains of bovine insulin, A and B, in 1952 and 1951, respectively. Prior to this it was widely assumed that proteins were somewhat amorphous. In determining these sequences, Sanger proved that proteins have a defined chemical composition. For this purpose he used the "Sanger Reagent", fluorodinitrobenzene (FDNB), to react with the exposed amino groups in the protein and in particular with the N-terminal amino group at one end of the polypeptide chain. He then partially hydrolysed the insulin into short peptides (either with hydrochloric acid or using an enzyme such as trypsin). The mixture of peptides was fractionated in two dimensions on a sheet of filter paper: first by electrophoresis in one dimension and then, perpendicular to that, by chromatography in the other. The different peptide fragments of insulin, detected with ninhydrin, moved to different positions on the paper, creating a distinct pattern which Sanger called "fingerprints". The peptide from the N-terminus could be recognised by the yellow colour imparted by the FDNB label and the identity of the labelled amino acid at the end of the peptide determined by complete acid hydrolysis and discovering which dinitrophenyl-amino acid was there. By repeating this type of procedure Sanger was able to determine the sequences of the many peptides generated using different methods for the initial partial hydrolysis. These could then be assembled into the longer sequences to deduce the complete structure of insulin. Finally, because the A and B chains are physiologically inactive without the three linking disulfide bonds (two interchain, one intrachain on A), Sanger and coworkers determined their assignments in 1955. Sanger's principal conclusion was that the two polypeptide chains of the protein insulin had precise amino acid sequences and, by extension, that every protein had a unique sequence. It was this achievement that earned him his first Nobel prize in Chemistry in 1958. This discovery was crucial for the later sequence hypothesis of Crick for developing ideas of how DNA codes for proteins.

Sequencing RNA

From 1951 Sanger was a member of the external staff of the Medical Research Council and when they opened the Laboratory of Molecular Biology in 1962, he moved from his laboratories in the Biochemistry Department of the university to the top floor of the new building. He became head of the Protein Chemistry division. Soon after his move he started looking at the possibility of sequencing RNA molecules and began developing methods for separating ribonucleotide fragments generated with specific nucleases. One of the problems was to obtain a pure piece of RNA to sequence. In the course of this he discovered in 1964, with Kjeld Marcker, the formylmethionine tRNA which initiates protein synthesis in bacteria. He was beaten in the race to be the first to sequence a tRNA molecule by a group led by Robert Holley from Cornell University who published the sequence of the 77 ribonucleotides of alanine tRNA from Saccharomyces cerevisiae in 1965. By 1967 Sanger's group had determined the nucleotide sequence of the 5S ribosomal RNA from Escherichia coli, a small RNA of 120 nucleotides.

Sequencing DNA

He then turned to sequencing DNA which would require an entirely different approach. He looked at different ways of using DNA polymerase I from E. coli to copy single stranded DNA. In 1975 together with Alan Coulson he published a sequencing procedure using DNA polymerase with radiolabelled nucleotides that he called the "Plus and Minus" technique. This involved two closely related methods that generated short oligonucleotides with defined 3' termini. These could be fractionated by electrophoresis on a polyacrylamide gel and visualised using autoradiography. The procedure could sequence up to 80 nucleotides in one go and was a big improvement on what gone before but was still very laborious. Nevertheless his group were able to sequence most of the 5,386 nucleotides of the single-stranded bacteriophage φX174. This was the first fully sequenced DNA-based genome. To their surprise they discovered that the coding regions of some of the genes overlapped with one another.

In 1977 Sanger and colleagues introduced the "dideoxy" chain-termination method for sequencing DNA molecules, also known as the "Sanger method". This was a major breakthrough and allowed long stretches of DNA to be rapidly and accurately sequenced. It earned him his second Nobel prize in Chemistry in 1980, which he shared with Walter Gilbert and Paul Berg. The new method was used by Sanger and colleagues to sequence human mitochondrial DNA (16,569 base pairs) and bacteriophage λ (48,502 base pairs). The dideoxy method was eventually used to sequence the entire human genome.

He is thus far (2012) the only person to have been awarded two Nobel Prizes in Chemistry, and one of only four two-time Nobel laureates: the other three were Marie Curie (Physics, 1903 and Chemistry, 1911), Linus Pauling (Chemistry, 1954 and Peace, 1962) and John Bardeen (twice Physics, 1956 and 1972).

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