A structure-function analysis to discover how receptor conformations and interactions determine semaphorin-neuropilin-plexin signalling outputs.

During the development of a multicellular organism cell guidance proteins interact with their cognate cell surface receptors to guide cells to their correct location. Such functions continue to be essential in the adult to maintain tissue homeostasis. Semaphorins use plexins as their main receptors for signalling and the semaphorin and plexin families together constitute one of the largest and functionally diverse of the cell guidance systems in vertebrates. We have gained some insight into the architecture and interactions which trigger semaphorin-plexin signalling, but fundamental questions remain and some of the most puzzling, and of potential clinical importance, concern the mechanisms of action of the secreted class 3 semaphorins (Sema3s), and their (co-)receptors. Neuropilin co-receptors play pivotal roles for Sema3 function and have been implicated in context dependent switching of cell guidance signalling outputs. There is an urgent need for information on molecular mechanism to underpin the design and interpretation of studies into biological function and clinical pathology. To advance the field we will combine structural biology and cellular imaging based approaches with functional studies (in house and in collaboration).The research plan is sub-divided into three inter-related sections that aim to discover:1. The structural determinants and mechanisms of action by which class 3 semaphorins exert differing effects on signalling.2. The conformational state of the plexin ectodomain in different contexts and its contribution to signal outcome.3. The mechanisms by which neuropilin binding can switch the outcomes of plexin signalling.Molecular level answers to the questions posed by semaphorin-neuropilin-plexin signalling will take us beyond the current state of the art, and impact on diverse disciplines, for example cellular immunology and developmental biology, as well as guiding the design of novel therapeutic agents.