Title: The structural biology of synaptic connectivity
Funder: Medical Research Council

Abstract: Central nervous system neurons, engaged in chemical synapses, are physically connected by an intricate protein network that spans the synaptic cleft to provide structural support and modulate bi­ directional signalling. For example, it is increasingly appreciated that post-synaptic neurotransmitter receptors interact across the synaptic cleft with pre-synaptic proteins, and that such "molecular bridges" crucially modulate their physiological functions. Our group has recently provided the first structural snapshots illustrating this principle (Elegheert et al, Science, 2016). The key target of our work is to understand in structural detail the higher order organization and functional meaning of increasingly complex trans­ synaptic assemblies, at both excitatory and inhibitory synapses. We build on a track record in structural analysis of GABA and glutamate receptors, cell adhesion molecules and receptor enzyme (phosphatases, kinases) and aim to answer key questions including: What are the rules of assembly in trans-synaptic complexes? How dynamic are such structures? How do they influence synapse formation, stability and synaptic transmission? We combine structural biology techniques (X-ray crystallography, single particle cryo-electron microscopy and cryo-electron tomography) and quantitative live cell fluorescence microscopy to define the architecture of these complexes in an environment as close as possible to physiological. We create structure-guided mutant constructs and test them in synapse formation assays and other functional paradigms (electrophysiology in whole cells and brain slices, and mouse models) in collaboration with specialist laboratories. Furthermore, by exploiting the modular architecture of soluble "synaptic organizer" proteins, we use structural information and domain recombination to create molecules with novel interaction properties. As an alternative, we design similar tools by specifically crosslinking nanobodies raised against synaptic receptors. These molecular tools allow manipulation of the number and properties of excitatory and inhibitory synapses in neuronal circuits, and the implementation of novel rules of synaptic communication and homeostatic plasticity, revealing the importance of specific neuronal connections. Defining the mechanisms of cognitive functions (such as learning, memory, thought, speech or consciousness) in cellular and molecular terms is certainly one of the big challenges in science but also of huge interest to society. We need to satisfy fundamental introspective questions (such as "How does my brain work?") but also hope to become capable of preventing, or delaying, age-related cognitive decline as well as curing neurological and psychiatric disorders. Disorders linked to synaptic dysfunction currently affect millions of people worldwide. This situation is likely to exacerbate considering the predicted increase of life expectancy worldwide. For example, within the UK, research commissioned by the Alzheimer's Society projects that the 2011 number of 750,000 people suffering from dementia may increase to 1million by 2021 and 1.7 million by 2051. A detailed understanding of the mechanisms that drive the formation, stability and function of CNS synapses would provide the solid grounding needed to develop novel therapies.


Research activity codes: 1.1 NORMAL BIOLOGICAL DEVELOPMENT AND FUNCTIONING
Health categories: NEUROLOGICAL