This chapter discusses the protein conformational changes in virus- cell fusion. With the techniques described in this chapter, it is possible to examine what happens to a relatively small region of the viral protein during its conformational change—that is, the loss of an antigenic epitope, or the exposure of a particular cleavage site or disulfide bond. Detailed kinetic studies, and perhaps the use of low temperatures, may reveal the sequence with which these rearrangements occur. In addition to describing aspects of the conformational change, it is necessary to ask whether the changes observed in an in vitro system are relevant for fusion in vitro. The conditions under which a given aspect of the conformational change occurs should reflect those under which fusion takes place. Most studies on the “acid” conformations of viral fusion proteins have examined structural changes that occur after acid treatment and reneutralization. The resulting structures may of course differ in important respects from the nascent molecules shortly after acid treatment. © 1993, Elsevier Inc. All rights reserved.
