Structural highlights
Function
[VP1_POVJC] Forms an icosahedral capsid with a T=7 symmetry and a 40 nm diameter. The capsid is composed of 72 pentamers linked to each other by disulfide bonds and associated with VP2 or VP3 proteins. Interacts with a N-linked glycoprotein containing terminal alpha(2-6)-linked sialic acids on the cell surface to provide virion attachment to target cell. The serotonergic receptor 5HT2AR also acts as a cellular receptor for JCV on human glial cells. Once attached, the virions enter predominantly by a ligand-inducible clathrin-dependent pathway and traffic to the ER. Inside the endoplasmic reticulum, the protein folding machinery isomerizes VP1 interpentamer disulfide bonds, thereby triggering initial uncoating. Next, the virion uses the endoplasmic reticulum-associated degradation machinery to probably translocate in the cytosol before reaching the nucleus. Nuclear entry of the viral DNA involves the selective exposure and importin recognition of VP2/Vp3 nuclear localization signal. In late phase of infection, neo-synthesized VP1 encapsulates replicated genomic DNA at nuclear domains called promyelocytic leukemia (PML) bodies, and participates in rearranging nucleosomes around the viral DNA.[1]
Publication Abstract from PubMed
JC polyomavirus (JCPyV) infection of immunocompromised individuals results in the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML). The viral capsid of JCPyV is composed primarily of the major capsid protein, virus protein 1 (VP1), and pentameric arrangement of VP1 monomers results in the formation of a pore at the five-fold axis of symmetry. While the presence of this pore is conserved among polyomaviruses, its functional role in infection or assembly is unknown. Here, we investigate the role of the five-fold pore in assembly and infection of JCPyV by generating a panel of mutant viruses containing amino acid substitutions to the residues lining this pore. Multicycle growth assays demonstrated that the relative fitness of all mutants was reduced, as compared to wild type virus. Bacterial expression of VP1 pentamers containing substitutions to residues lining the five-fold pore did not affect pentamer assembly or prevent association with the minor capsid protein VP2. The X-ray crystal structures of selected pore mutants contained subtle changes to the five-fold pore, and no other changes to VP1 were observed. Pore-mutant pseudoviruses were not deficient in assembly, packaging of the minor capsid proteins, binding to cells, or in transport to the host cell endoplasmic reticulum. Instead, these mutant viruses were unable to expose VP2 upon arrival to the endoplasmic reticulum, a step that is critical for infection. This study demonstrates that the five-fold pore is an important structural feature of JCPyV and minor modifications to this structure has significant impacts on infectious entry. IMPORTANCE: JCPyV is an important human pathogen that causes a severe neurological disease in immunocompromised individuals. While the high resolution X-ray structure of the major capsid protein of JCPyV has been solved, the importance of a major structural feature of the capsid, the five-fold pore, remains poorly understood. This pore is conserved across polyomaviruses and suggests that these viruses have either limited structural plasticity in this region or that this pore is important in infection or assembly. Using a structure-guided mutational approach, we showed that modulation of this pore severely inhibits JCPyV infection. These mutants do not appear deficient in assembly or early steps in infectious entry and are instead reduced in their ability to expose a minor capsid protein in the host cell endoplasmic reticulum. Our work demonstrates that the five-fold pore is an important structural feature for JCPyV.
Modulation of a pore in the capsid of JC polyomavirus reduces infectivity and prevents exposure of the minor capsid proteins.,Nelson CD, Stroh LJ, Gee GV, O'Hara BA, Stehle T, Atwood WJ J Virol. 2015 Jan 21. pii: JVI.00089-15. PMID:25609820[2]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Pho MT, Ashok A, Atwood WJ. JC virus enters human glial cells by clathrin-dependent receptor-mediated endocytosis. J Virol. 2000 Mar;74(5):2288-92. PMID:10666259
- ↑ Nelson CD, Stroh LJ, Gee GV, O'Hara BA, Stehle T, Atwood WJ. Modulation of a pore in the capsid of JC polyomavirus reduces infectivity and prevents exposure of the minor capsid proteins. J Virol. 2015 Jan 21. pii: JVI.00089-15. PMID:25609820 doi:http://dx.doi.org/10.1128/JVI.00089-15
