Aaron Klug

Engineering zinc finger proteins (ZFPs) for the regulation of gene expression

Aaron Klug joined the newly-built LMB in 1962, moving from Birkbeck College, London where he had worked with Rosalind Franklin on the structure of tobacco mosaic virus. He continued to work on this helical virus, and also on the structures of spherical viruses, establishing many of the basic rules governing their structure and self-assembly. His group was also the first to determine the structure of a tRNA, work which would later lead him to the analysis of RNA enzymes or 'ribozymes'.

He was the Director of the Lab from 1986 to 1996, and President of the Royal Society from 1995 to 2000.

Arguably his most important contribution to scientific research was his painstaking development of crystallographic electron microscopy. This combines the techniques of electron microscopy and X-ray diffraction to recover three-dimensional structural information from two-dimensional electron micrographs. In this way, he and others were able to reveal the structures of complex biological materials not amenable to conventional X-ray crystallography alone. For this work, he received the Nobel Prize in Chemistry in 1982.

Aaron was also the discoverer of zinc-finger proteins, a class of proteins which bind specific DNA sequences by means of arrays of 'fingers', each of which interacts with a run of three or four base pairs. The modular nature of these proteins has made it possible to design synthetic proteins with a wide range of specificities, opening the prospect of targeted therapies for a wide range of diseases.

It has long been the goal of molecular biologists to design DNA binding proteins for the specific control of gene expression. The zinc finger design which I discovered 20 years ago is ideally suited for such purposes, discriminating between closely related sequences both in vitro and in vivo. Whereas other DNA binding proteins generally make use of the 2-fold symmetry of the double helix, zinc fingers do not, and so can be linked linearly in tandem to recognize DNA sequences of different lengths, with high fidelity and affinity.

This modular design offers a large number of combinatorial possibilities for the specific recognition of DNA.

By fusing zinc finger peptides to effector domains, genes can be selectively targeted and switched off or on and variously manipulated.

Over the years we learned to engineer longer runs of fingers to form ZFPs which give virtually single gene specifity in the human genome. These longer peptides are assembled out of libraries of 2- or 3-finger peptides, originally developed at the LMB, and now held by the biotech company Sangamo Biosciences after they acquired our MRC spin-off company, Gendaq. I am on the Scientific Advisory Board of Sangamo. Sangamo have recently begun clinical trials using VEGF-activating ZFPs to treat human peripheral arterial disease by stimulating vascular growth.

Other examples of therapeutic development programs are those on neuropathic pain, macular degeneration and producing permanently modified uninfectable T-cells to combat both HIV and opportunistic infections.

Also in progress are pre-clinical studies using ZFP nucleases to target the defective genes in two monogenic disorders, Severe Combined Immunodeficiency and sickle-cell anaemia. The aim is to replace the mutant sequence in each case by a correct copy from an extrachromosomal DNA donor by means of homologous recombination. Promising results have been reported.

Published research