Receptor activity modifying proteins (RAMPs) associate with a number of G-protein coupled receptors (GPCRs). They are essential for the binding of the native peptide agonists at CGRP, adrenomedullin and amylin receptors; at other GPCRs they can promote cell surface delivery or modulate signal transduction. Thus they are key receptor components and proven drug targets. Guided by a crystal structure of the extracellular N-terminus of RAMP1, mutagenesis has revealed how it associates with the GPCR, calcitonin receptor-like receptor (CLR) to form a CGRP receptor. However, little is known about the structure- activity relationship for the two other RAMPs, RAMP2 and RAMP3. These are essential for the formation of adrenomedullin receptors. We have produced models for RAMP2 and RAMP3 and have purified these proteins to homogeneity. In this application, we will combine all our information to guide mutagenesis to understand how RAMP2 interacts with CLR to form a receptor for adrenomedullin. We wi ll also carry out structural characterisation of RAMPs with CLR. The work will provide new information on the functioning of the RAMP family and will facilitate drug discovery at receptors involving RAMPs. Natural ligands such as hormones and neurotransmitters largely produce their effects by acting at proteins on the surface of cells known as receptors; drugs work by binding to these receptors to either mimic the natural transmitter or reduce its action. It is important to know the structure of receptors, to understand basic biological processes and to design new drugs. Receptor activity modifying proteins (RAMPs) are a family of three proteins that interact with many important receptors, frequen tly receptors for which it has been difficult to discover drugs. A new class of antimigraine drug works by binding, in part, to RAMP1. RAMP 2 and 3 form parts of receptors involved in control of blood pressure, blood vessel growth and also appetite. If we knew more about RAMPs, this would help drug discovery as well as increasing our fundamental knowledge of physiology. This project will investigate the structure of RAMPs by biophysical techniques. It will investigate how they can bind to recept ors and how, in turn, natural ligands can bind to them once they are part of a receptor complex. This will help the design of new drugs to treat diverse conditions.