25 November 2013
ByAppeared in BioNews 732
Fred Sanger, renowned biochemist, has died aged 95. Having pioneered seminal techniques for the understanding of both proteins and DNA, Dr Sanger is widely hailed as one of the most influential scientists of recent years.
He is one of only four people to receive two Nobel Prizes, and the only person among those to receive both in Chemistry.
Dr Sanger began his career at the University of Cambridge, UK, where he undertook his undergraduate and postgraduate studies, after which he began the work that would earn him his first Nobel Prize. Dr Sanger had developed a method to determine the order of amino acids in a protein, which he used to 'sequence' insulin.
Sanger's method involved using a chemical reagent – DNFB – that only reacts with amino acids at one end of a protein chain – the 'amino' end. He used this chemical to label insulin, before breaking it up into the individual amino acids, selecting out the labelled ones and seeing which amino acid they were.
Inspection of the DNFB-labelled components revealed there were two different amino acids present, and hence two polypeptide chains in the insulin protein. By fragmenting these chains into different length stretches of amino acids, and then using DNFB again, he was able to deduce the exact order of all of the amino acids in both chains, as well as how the chains were joined together.
This was the first time such a feat had been accomplished, providing a protocol and rationale which could be applied to all proteins. Moreover, it helped reveal the relationship between the structure and function of proteins, hugely increasing our understanding of these important molecules.
In 1962 he moved to the Laboratory of Molecular Biology (LMB), an institution with a long history of Nobel laureates. Here, he began to apply himself to solving a comparable problem with a completely different type of molecule; how to sequence the nucleic acids, RNA and DNA, which encode our genetic information.
The technique he developed was known as the chain-termination, or 'dideoxy' method. In this method, DNA to be sequenced is copied using the enzyme DNA polymerase, which incorporates the DNA nucleotide – or bases – into the growing chain. The trick of Sanger's method was to also include modified versions of each of the bases – so called dideoxy nucleotides – at very low concentrations. Dideoxy bases lack a certain chemical group required for addition of subsequent bases; thus addition of a dideoxy base stops that chain of DNA from growing.
Sanger labelled each different dideoxy base with radioactivity, and then performed four different DNA polymerase reactions, each with a different labelled chain-terminator present (A, C, T or G), before using a technique to separate the produced DNA molecules based on their lengths. By 'reading' from the shortest chain to the longest, he was able to see the order of the DNA bases in the original chain, by seeing in which reaction the radioactivity was present for a given nucleotide.
It is from this technique that Sanger became known as the 'father of genomics', having used it to sequence an entire viral genome, followed by the genome of human mitochondria, the component of our cells responsible for producing energy. Not only did this represent the first genome sequenced and the first instalment of the human genome respectively, his technology was later automated, and went on to be used to produce the first draft of the Human Genome Project.
'It is simply impossible to overestimate the impact he has had on modern genetics and molecular biology', said Dr Venki Ramakrishnan, current Deputy Director of the LMB. 'Moreover, by his modest manner and his quiet and determined way of carrying out experiments himself right to the end of his career, he was a superb role model and inspiration for young scientists everywhere'.
Few biologists in the last century can claim to have had such far reaching impact as Fred Sanger. The DFNB reagent he used to label amino groups for protein sequencing, the dideoxy method of DNA sequencing, and the Wellcome Trust funded centre of British genomics have all adopted his name, a telling marker of how indelibly he has contributed to science.
Perhaps the most fitting tribute came on Twitter, from science writer Ed Yong, who posted:
This message was written in the language of DNA, which encode the amino acids that form protein chains. Combining the two biological languages that Sanger taught us how to read, this simply translates to:
'R I P F R E D S A N G E R'.