Structural Comparison of Insect RNA Viruses
Manidipa Banerjee, Jeffrey A Speir and John E Johnson
from: Insect Virology (Edited by: Sassan Asgari and Karyn N. Johnson). Caister Academic Press, U.K. (2010)
In recent years, small insect RNA viruses with non-enveloped capsids, such as members of the Nodaviridae, Tetraviridae, Dicistroviridae and Cypoviridae families, have been characterized using X-ray crystallography or cryoelectron microscopy. The capsids of these viruses are icosahedral, with diameters of 30 - 70 nm, and triangulation numbers ranging from 1 to 4 (T=1 to T=4). Viruses packaging single stranded RNA such as nodaviruses, tetraviruses and dicistroviruses contain capsid proteins with closely similar cores comprising an antiparallel β-barrel, jellyroll fold. These capsid proteins undergo analogous post-assembly autocatalytic maturation cleavage. Tetraviruses are unique among this group in containing an immunoglobulin-like domain inserted in their jellyroll capsid proteins, and in undergoing large conformational changes during maturation. Cypoviruses, which package double stranded RNA, have T=2 capsids with structural similarities to the inner shell of reovirus particles. Structural studies of insect RNA viruses have provided valuable information regarding the principles of icosahedral capsid formation, genomic RNA organization, RNA-protein interaction, the mechanism of maturation and associated conformational changes, and the positioning of virus-encoded membrane lytic peptides in capsids. This has resulted in compelling hypotheses regarding capsid disassembly and RNA translocation during infection, some of which have been validated using biochemical and biological studies read more ...