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Structure of the VP5*/VP8* assembly from the human rotavirus strain CDC-9 - Reversed conformation
Structural highlights
FunctionX4YMN0_9REOV Outer capsid protein VP4: Spike-forming protein that mediates virion attachment to the host epithelial cell receptors and plays a major role in cell penetration, determination of host range restriction and virulence. Rotavirus attachment and entry into the host cell probably involves multiple sequential contacts between the outer capsid proteins VP4 and VP7, and the cell receptors. It is subsequently lost, together with VP7, following virus entry into the host cell. Following entry into the host cell, low intracellular or intravesicular Ca(2+) concentration probably causes the calcium-stabilized VP7 trimers to dissociate from the virion. This step is probably necessary for the membrane-disrupting entry step and the release of VP4, which is locked onto the virion by VP7. During the virus exit from the host cell, VP4 seems to be required to target the newly formed virions to the host cell lipid rafts.[HAMAP-Rule:MF_04132] Outer capsid protein VP5*: Forms the spike 'foot' and 'body' and acts as a membrane permeabilization protein that mediates release of viral particles from endosomal compartments into the cytoplasm. During entry, the part of VP5* that protrudes from the virus folds back on itself and reorganizes from a local dimer to a trimer. This reorganization may be linked to membrane penetration by exposing VP5* hydrophobic region. In integrin-dependent strains, VP5* targets the integrin heterodimer ITGA2/ITGB1 for cell attachment.[HAMAP-Rule:MF_04132] Outer capsid protein VP8*: Forms the head of the spikes and mediates the recognition of specific host cell surface glycans. It is the viral hemagglutinin and an important target of neutralizing antibodies. In sialic acid-dependent strains, VP8* binds to host cell sialic acid, most probably a ganglioside, providing the initial contact. In some other strains, VP8* mediates the attachment to histo-blood group antigens (HBGAs) for viral entry.[HAMAP-Rule:MF_04132] Publication Abstract from PubMedRotavirus live-attenuated vaccines, both mono- and pentavalent, generate broadly heterotypic protection. B-cells isolated from adults encode neutralizing antibodies, some with affinity for VP5*, that afford broad protection in mice. We have mapped the epitope of one such antibody by determining the high-resolution cryo-EM structure of its antigen-binding fragment (Fab) bound to the virion of a candidate vaccine strain, CDC-9. The Fab contacts both the distal end of a VP5* beta-barrel domain and the two VP8* lectin-like domains at the tip of a projecting spike. Its interactions with VP8* do not impinge on the likely receptor-binding site, suggesting that the mechanism of neutralization is at a step subsequent to initial attachment. We also examined structures of CDC-9 virions from two different stages of serial passaging. Nearly all the VP4 (cleaved to VP8*/VP5*) spikes on particles from the earlier passage (wild-type isolate) had transitioned from the "upright" conformation present on fully infectious virions to the "reversed" conformation that is probably the end state of membrane insertion, unable to mediate penetration, consistent with the very low in vitro infectivity of the wild-type isolate. About half the VP4 spikes were upright on particles from the later passage, which had recovered substantial in vitro infectivity but had acquired an attenuated phenotype in neonatal rats. A mutation in VP4 that occurred during passaging appears to stabilize the interface at the apex of the spike and could account for the greater stability of the upright spikes on the late-passage, attenuated isolate. IMPORTANCE Rotavirus live-attenuated vaccines generate broadly heterotypic protection, and B-cells isolated from adults encode antibodies that are broadly protective in mice. Determining the structural and mechanistic basis of broad protection can contribute to understanding the current limitations of vaccine efficacy in developing countries. The structure of an attenuated human rotavirus isolate (CDC-9) bound with the Fab fragment of a broadly heterotypic protective antibody shows that protection is probably due to inhibition of the conformational transition in the viral spike protein (VP4) critical for viral penetration, rather than to inhibition of receptor binding. A comparison of structures of CDC-9 virus particles at two stages of serial passaging supports a proposed mechanism for initial steps in rotavirus membrane penetration. Rotavirus VP4 Epitope of a Broadly Neutralizing Human Antibody Defined by Its Structure Bound with an Attenuated-Strain Virion.,Jenni S, Li Z, Wang Y, Bessey T, Salgado EN, Schmidt AG, Greenberg HB, Jiang B, Harrison SC J Virol. 2022 Aug 24;96(16):e0062722. doi: 10.1128/jvi.00627-22. Epub 2022 Aug 4. PMID:35924923[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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