Editor exposed: XRD provides evidence

Combined effort

A combination of traditional X-ray crystallography and computer-based model reported in the journal Science have uncovered the structure of an important gene-editing protein.

Plant pathologist and microbiologist Adam Bogdanove of Iowa State University and former graduate student Matthew Moscou discovered how a class of proteins from plant pathogenic bacteria find and bind specific sequences in plant genomes two and a half year ago. Since then, researchers across the globe have been moving fast to exploit their discovery.

A TALEN for fusion

Indeed, in 2011, it was demonstrated that these proteins could fuse to DNA modifying enzymes and then manipulate genes and gene functions. These fused proteins, TAL effector nucleases, or TALENs, can open up new insights into gene function in plants and animals and be used to improve, for instance, specific traits in livestock and plants such as disease resistance. There is even the possibility that in the long term, the research might provide advances in treating human genetic disorders, Bogdanove suggests. The ease with which these proteins can be genetically engineered to bind DNA sequences of choice has itself led to a flurry of research publications demonstrating their potential in a wide range of cells types, including human stem cells.

In December 2011, the journal Nature Methods named gene editing with engineered nucleases as its "Method of the Year". Now, Bogdanove and researchers from the Fred Hutchinson Cancer Research Center in Seattle have taken the next step in this field by determining the three-dimensional crystal structure of a TAL effector bound to DNA.

Writing in Science Express, the online preprint version of the journal Science, the team, which includes post-doctoral worker Amanda Mak from the Hutchinson Center and fellow post-doc Andres Cernadas in Bogdanove's lab, were able to visualize the shape of TAL effectors and how they physically interact with the double helix of DNA. The work provides scientists with a clearer understanding of the biochemistry underlying the ability of these molecules to recognize and stick to specific DNA sequences. Such understanding has implications for improving our ability to target the proteins to different locations in a genome and to better predict and prevent their binding to unintended, off-target sites Bogdanove believes.

Bogdanove adds that the crystal structure itself is also interesting simply from a fundamental biological perspective. "It is really quite beautiful," he says, "So far there is nothing else in nature quite like it." The structure determination was carried out in collaboration with Hutchinson scientists Barry Stoddard, an expert in protein DNA interactions, and Phil Bradley, a computational biologist. The complete determination and molecular modelling took a year to undertake.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.