ERC FUNDED PROJECTS

Following their synthesis during DNA replication, sister chromatids remain paired by the cohesin complex, which forms the basis for their faithful segregation during cell division. Cohesin is a large ring-shaped protein complex, incorporating an ABC-type ATPase module. Despite its importance for genome stability, the molecular mechanism of cohesin action remains as intriguing as it remains poorly understood. How is cohesin topologically loaded onto chromatin? How is it unloaded again? What happens to cohesin during DNA replication in S-phase, so that it establishes cohesion between newly synthesized sister chromatids? We propose to capitalise on our recent success in the biochemical reconstitution of topological cohesin loading onto DNA. This lays the foundation for a work programme encompassing a combination of biochemical, single molecule, structural and genetic approaches to address the above questions. Five work packages will investigate cohesin’s molecular behaviour during its life-cycle on chromosomes, including the ATP binding and hydrolysis-dependent conformational changes that make this molecular machine work. It will be complemented by mechanistic analyses of the cofactors that help cohesin to load onto chromosomes and establish sister chromatid cohesion. The insight gained will not only advance our molecular knowledge of sister chromatid cohesion. It will more generally advance our understanding of the ubiquitous family of chromosomal SMC ATPases, of which cohesin is a member, and their activity of shaping and segregating genomes.

2 120 100 €

Start date: 2015-10-01, End date: 2020-09-30

The unexpected connection between the primary cilium and cell-to-cell signalling is one of the most exciting discoveries in cell and developmental biology in the last decade. In particular, the Hedgehog (Hh) pathway relies on the primary cilium to fulfil its fundamental functions in orchestrating vertebrate development. This microtubule-based antenna, up to 5 µm long, protrudes from the plasma membrane of almost every human cell and is the essential compartment for the entire Hh signalling cascade. All its molecular components, from the most upstream transmembrane Hh receptor down to the ultimate transcription factors, are dynamically localised and enriched in the primary cilium. The aim of this proposal, which combines structural biology and live cell imaging, is to understand the function and signalling consequences of the multivalent interactions between Hh signal transducer proteins as well as their spatial and temporal regulation in the primary cilium. The key questions my laboratory will address are: What are the rules for assembly of Hh signal transduction complexes? How dynamic are these complexes in size and organisation? How are these processes linked to the transport and accumulation in the primary cilium? I will combine state-of-the art structural biology techniques (with an emphasis on X-ray crystallography) to study the molecular architecture of binary and higher-order Hh signal transduction complexes and live cell fluorescence microscopy (for protein localisation and direct protein interactions). These two approaches will allow me to identify and define specific protein-protein interfaces at the atomic level and test their functional consequences in the cell in real time. My goal is to consolidate a world-class morphogen signal transduction laboratory, deciphering fundamental biological insights. Importantly, my results and reagents can potentially feed into the development of novel anti-cancer therapeutics and reagents promoting stem cell therapy.

1 727 456 €

Start date: 2015-08-01, End date: 2020-07-31

Excising a membrane protein from its natural environment, preserving the lipid bilayer, and characterising the lipids that surround it is the ‘holy grail’ of membrane protein biophysics. However, with some 40,000 different lipid structures the challenges we face in understanding selective binding arise not just from the complexity and dynamics of the lipidome, but also from the transient nature of protein lipid interactions. To overcome these challenges we will take mass spectrometry (MS) into a new era, allowing, for the first time, the study of proteins in an environment as close as possible to the natural one. To do this we will (i) characterise protein lipid interactions by employing a high resolution Orbitrap mass spectrometer developed in-house, specifically for membrane proteins, (ii) capture the native lipid environment in vehicles suitable for use in conjunction with MS, and (iii) establish a new platform to be known as integral membrane protein desorption electrospray ionization (impDESI). Designed and built in-house impDESI is capable of releasing membrane proteins from surfaces directly into the mass spectrometer (MS). We will develop impDESI for membrane mimetics, and subsequently portions of natural membranes, enabling us to extract proteins with oligomeric state preserved and native lipid binding intact. The development of impDESI, in conjunction with high resolution Orbitrap MS, and coupled with the optimisation of membrane mimetics, has the potential to radically transform our understanding of native lipid binding, not only directly, but also temporally and spatially. Together these advances will answer key questions about how lipids modulate protein interfaces, occupy different binding sites, modulate membrane protein structure and modify function in vivo. Given the importance of membrane proteins as potential drugs targets understanding their modulation by lipids would be a major step towards more effective drug development.

2 481 744 €

Start date: 2016-06-01, End date: 2021-05-31

Fusion of two biological membranes is essential to life. It is required during organism development, for trafficking of material between cellular compartments, for transfer of information across synapses, and for entry of viruses into cells. Fusion must be carefully controlled and the core fusion components are typically found within a complex regulatory machine. There have been decades of research on the structure and function of individual components, on the dynamics and biophysics of fusion, and on phenotypes resulting from mutating or inhibiting component proteins. These have led to a model for fusion in which regulated refolding or assembly of proteins draws two membranes closer together until they fuse. Despite this breadth of study, we know very little about how the components of the fusion machinery function in context: How are they arranged on the membrane around the site of fusion? How do they respond structurally to regulation? How does the fully assembled machinery rearrange to reshape the membrane and drive fusion? These gaps in knowledge can be attributed to a shortage of structural biology methods able to derive structural data on proteins assembled within complex, heterogeneous or dynamic environments such as a fusion site. Here I propose to apply a combination of state-of-the-art cryo-electron tomography, image processing and correlative fluorescence and electron microscopy methods to obtain detailed structural information on assembled fusion machineries and of fusion intermediates both in vitro and in vivo. I will study how influenza virus fuses with a target membrane, complemented by studies on fusion of HIV-1 and of synaptic vesicles. By determining how viral and synaptic fusion complexes reposition and restructure prior to fusion, how they arrange around the fusion site, how they reshape the membrane to induce fusion, and how these processes can be regulated and inhibited, I will derive a mechanistic model of membrane fusion in situ.

1 965 961 €

Start date: 2015-09-01, End date: 2021-08-31