Cover photograph (Copyright © 2003, American Society for Microbiology. All Rights Reserved.): Receptor binding-induced conformational change of Newcastle disease virus hemagglutinin-neuraminidase (HN) protein. A comparison of the HN structure crystallized alone or in complex with 2-deoxy-2,3-dehydro-N-acetylneuraminic acid revealed substantial conformational changes in a limited region. The chains are colored according to the root mean square deviation of the α-carbon atoms between the two crystal forms of HN. The red regions represent those that move more than 0.5 Å. The chief structural changes lie between the receptor-binding pocket and the large hydrophobic area that is essential for the fusion-promotion activity of HN. (See related article in December 2002: vol. 76, no. 24, p. 13028.)