ayout 1 - EMBL Grenoble

EMBL Research at a Glance 2009
Daniel Panne
PhD 1999, University of
Basel.
Postdoctoral research at
Harvard University, Boston.
Group leader at EMBL
Grenoble since 2007.
Integrating signals through complex assembly
Previous and current research
Most cellular processes depend on the action of large multi-subunit complexes, many of which are
assembled transiently and change their shape and composition during their functional cycle. The
modular nature of the components, as well as their combinatorial assembly, can generate a large
repertoire of regulatory complexes and signalling circuits. The characterisation and visualisation
of such cellular structures is one of the most important challenges in molecular biology today.
Characterisation of multicomponent systems requires expertise in a number of techniques including
molecular biology, biochemistry, biophysics, structural biology and bioinformatics. We
visualise cellular entities using low-resolution imaging techniques such as electron microscopy
(EM) and small angle X-ray scattering (SAXS) or high-resolution techniques such as NMR and
macromolecular X-ray crystallography (figure 1).
The systems we have been studying are involved in transcriptional regulation. Transcriptional regulation
is mediated by transcription factors which bind to their cognate sites on DNA, and through
their interaction with the general transcriptional machinery, and/or through modification of chromatin
structure, activate or repress the expression of a nearby gene. The so-called ‘cis-regulatory
code’, the array of transcription factor binding sites, is thought to allow read-out and signal processing of cellular signal transduction cascades.
Transcriptional networks are central regulatory systems within cells and in establishing and maintaining specific patterns of gene expression.
One of the best-characterised systems is that of the interferon-β promoter. Three different virus-inducible signalling pathways are integrated
on the 60 base pair enhancer through coassembly of eight ‘generic’ transcription factors to form the so-called ‘enhanceosome’, which is thought
to act as a logic AND gate. The signal transducing properties are thought to reside in the cooperative nature of enhanceosome complex assembly.
To understand the signal transducing properties of the enhanceosome, we have determined co-crystal structures that give a complete view
of the assembled enhanceosome structure on DNA (figure 2). The structure shows that association of the eight proteins on DNA creates a continuous
surface for the recognition of the enhancer sequence. Our structural analysis gives us, for the first time, detailed insights into the structure
of an enhanceosome and yields important insight into the design and architecture of such higher-order signalling assemblies.
Future projects and goals
We are particular interested in understanding the signal processing through higher order assemblies. As such, the enhanceosome has served
as a paradigm for understanding signal integration on higher eukaryotic enhancers. The interferon (IFN) system is an extremely powerful antiviral
response and central to innate immunity in humans. Most serious viral human pathogens have evolved tools and tricks to inhibit the IFN
response. Many viruses do so by producing proteins that interfere with different parts of the IFN system. Therefore, our studies are of fundamental
interest to understand important signal processing pathways in the cell and may also point to better methods of controlling virus infections;
for example, novel anti-viral drugs might be developed which prevent viruses from circumventing the IFN response. Misregulation
of IFN signalling pathways is also involved in inflammation and cancer and is therefore of fundamental importance for human health. We will
also expand our multiprotein crystallisation strategies to complexes involved in modification of chromatin structure.
Figure 1 (left): We employ a
number of different resolution
techniques to visualise cellular
structures.
Figure 2 (right): Atomic model of
the INF-b enhanceosome.
Selected references
Panne, D. (2008). The enhanceosome. Curr. Opin. Struct. Biol., 18,
236-2
Panne, D., Maniatis, T. & Harrison, S.C. (2007). An atomic model of
the interferon-beta enhanceosome. Cell, 129, 1111-1123
9
Panne, D., McWhirter, S.M., Maniatis, T. & Harrison, S.C. (2007).
Interferon regulatory factor 3 is regulated by a dual phosphorylationdependent
switch. J. Biol. Chem., 282, 22816-22822
Panne, D., Maniatis, T. & Harrison, S.C. (200). Crystal structure of
ATF-2/c-Jun and IRF-3 bound to the interferon-β enhancer. EMBO
J., 23, 38-393