Figure 1: Netrin-1 is a guidance molecule that steers axons to their targets and guides the branching of blood vessels to starving tissue. The crystal structure of netrin-1 in complex with its cell surface receptor DCC (Deleted in Colorectal Cancer) shown here provides a structural basis for the clustering of DCC by netrin-1. The structure also suggests that DCC can be replaced by other cell surface receptors, leading to different signalling outcomes.
The Meijers group investigates signalling mechanisms across the cell membrane using integrated structural biology and biophysical techniques.
Previous and current research
Receptor signalling in axon guidance
Many single-pass transmembrane receptors signal through association with other receptors, passing extra-cellular cues through the membrane to cytosolic signalling pathways. We have established mammalian expression technologies to produce large quantities of receptor fragments and ligands. Complexes between fragments of receptors and their ligands are characterised by crystallography, SAXS and electron microscopy, giving a holistic view of single-pass membrane receptor signalling.
We have determined the crystal structure of the guidance molecule netrin-1 in complex with a fragment of the deleted in colorectal cancer (DCC) receptor (Finci et al., 2014), revealing how the external cue netrin-1 brings two DCC receptors in close proximity, leading to the propagation of a signal across the cell membrane. This has dramatic effects, causing an axon to change its course or undergo apoptosis. Netrin-1 is capable of binding and combining several receptors, and we believe that this occurs through a generic receptor binding site that involves small molecules. These small molecules help to select certain receptors, thereby influencing signalling outcomes. We are in the process of identifying these small molecules and investigating how the other receptors bind to netrin-1.
Integrated sample preperation and characterisation (SPC) at the synchrotron beamlines
The SPC facility has been built to deliver a sample handling environment close to the beamlines. Users can process samples just before accessing the beamlines, using a range of biophysical techniques for sample purification and characterisation. Project-based access is available for extensive sample characterisation and optimisation. We provide a large state-of-the-art crystallisation facility, thermal shift assays for sample optimisation and standardised quality control protocols including mass spectrometry analysis.
Future Projects and Goals
We will investigate other cell surface receptor signalling hubs to study how external morphogens can affect signalling across the cell membrane. We will focus on signalling systems that affect cell migration, since this affects fundamental processes in tissue development. Netrin-1, for instance, is thought to play an important role in the regulation of cell proliferation and the prevention of tumour metastasis. We would like to understand which factors contribute to netrin induced signaling, to help in the design of new therapies for controlled cell migration.
To further enhance the versatility in sample handling and characterisation at the PETRA III beamlines, we will develop new integrated sample environment setups. The miniaturisation and automation of the macromolecular crystallography and SAXS beamlines has led to an increase in sample throughput to such an extent, that it becomes worthwhile to integrate complementary sample manipulation on or near the beamlines. The standardisation of quality control, purification and sample delivery allows the users to handle more challenging samples on site, and to make better informed decisions about their experiments in real time.