ABSTRACT
This chapter aims to bring together data concerning decay-accelerating factor (CD55) structure with a mass of functional data relating to the full range of its biological interactions to give our most complete view of the biology of this fascinating molecule. CD55 is an extracellular glycoprotein with an Mr of approximately 70,000 attached to the cell membrane by a glycosyl phosphatidylinositol anchor. The three sets of structures provide different snapshots of CD55 architecture, but for the biologist the important issue must be how to combine the information from all of these to give the most accurate description for the four short consensus repeat domains. The three sets of X-ray structures are: CD5534, CD5523, and CD551234. Mutation of CD55 has proved a powerful technique to illuminate parts of the molecule responsible for conferring decay acceleration. The structures determined to date have begun to illuminate relationships between the various biological roles of this molecule and the underlying atomic structure.
