Two Epstein-Barr virus glycoprotein complexes.
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B-Lymphocytes↗
Biomedical subjects
C M Lake
Publications and source records attributed to C M Lake.
Epstein-Barr virus gH is essential for penetration of B cells but also plays a role in attachment of virus to epithelial cells.
Entry of Epstein-Barr virus (EBV) into B cells is initiated by attachment of glycoprotein gp350 to the complement receptor type 2 (CR2). A complex of three glycoproteins, gH, gL, and gp42, is subsequently required for penetration. Gp42 binds to HLA class II, which functions as an entry mediator or coreceptor and, by analogy with other herpesviruses, gH is then thought to be involved virus-cell fusion. However, entry of virus into epithelial cells is thought to be different. It can be initiated by attachment by an unknown glycoprotein in the absence of CR2. There is no interaction between gp42 and HLA class II and instead a distinct complex of only the two glycoproteins gH and gL interacts with a novel entry mediator. Again, by analogy with other viruses gH is thought to be critical to fusion. To investigate further the different roles of gH in infection of the two cell types and to examine its influence on the assembly of the gH-gL-gp42 complex, we constructed two viruses, one in which the gH open reading frame was interrupted by a cassette expressing a neomycin resistance gene and the gene for green fluorescent protein and one as a control in which the neighboring nonessential thymidine kinase gene was interrupted with the same cassette. Virus lacking gH exited from cells normally, although loss of gH resulted in rapid turnover of gL and gp42 as well. The virus bound normally to B lymphocytes but could not infect them unless cells and bound virus were treated with polyethylene glycol to induce fusion. In contrast, virus that lacked the gH complex was impaired in attachment to epithelial cells and the effects of monoclonal antibodies to gH implied that this resulted from loss of gH rather than other members of the complex. These results suggest a role for gH in both attachment and penetration into epithelial cells.
Animals↗
Epstein-Barr virus that lacks glycoprotein gN is impaired in assembly and infection.
The Epstein-Barr virus (EBV) glycoproteins N and M (gN and gM) are encoded by the BLRF1 and BBRF3 genes. To examine the function of the EBV gN-gM complex, recombinant virus was constructed in which the BLRF1 gene was interrupted with a neomycin resistance cassette. Recombinant virus lacked not only gN but also detectable gM. A significant proportion of the recombinant virus capsids remained associated with condensed chromatin in the nucleus of virus-producing cells, and cytoplasmic vesicles containing enveloped virus were scarce. Virus egress was impaired, and sedimentation analysis revealed that the majority of the virus that was released lacked a complete envelope. The small amount of virus that could bind to cells was also impaired in infectivity at a step following fusion. These data are consistent with the hypothesis that the predicted 78-amino-acid cytoplasmic tail of gM, which is highly charged and rich in prolines, interacts with the virion tegument. It is proposed that this interaction is important both for association of capsids with cell membrane to assemble and release enveloped particles and for dissociation of the capsid from the membrane of the newly infected cell on its way to the cell nucleus. The phenotype of EBV lacking the gN-gM complex is more striking than that of most alphaherpesviruses lacking the same complex but resembles in many respects the phenotype of pseudorabies virus lacking glycoproteins gM, gE, and gI. Since EBV does not encode homologs for gE and gI, this suggests that functions that may have some redundancy in alphaherpesviruses have been concentrated in fewer proteins in EBV.
B-Lymphocytes↗
The Epstein-Barr virus (EBV) gN homolog BLRF1 encodes a 15-kilodalton glycoprotein that cannot be authentically processed unless it is coexpressed with the EBV gM homolog BBRF3.
The Epstein-Barr virus (EBV) homolog of the conserved herpesvirus glycoprotein gN is predicted to be encoded by the BLRF1 open reading frame (ORF). Antipeptide antibody to a sequence corresponding to residues in the predicted BLRF1 ORF immunoprecipitated a doublet of approximately 8 kDa from cells expressing the BLRF1 ORF as a recombinant protein. In addition, four glycosylated proteins of 113, 84, 48, and 15 kDa could be immunoprecipitated from virus-producing cells by the same antibody. The 15-kDa species was the mature form of gN, which carried alpha2,6-sialic acid residues. The remaining glycoproteins which associated with gN were products of the BBRF3 ORF of EBV, which encodes the EBV gM homolog. The 8-kDa doublet seen in cells expressing recombinant gN comprised precursors of the mature 15-kDa gN. Coexpression of EBV gM with EBV gN was required for authentic processing of the 8-kDa forms to the 15-kDa form.
Genes, Viral↗
Poly(adenosine diphosphate ribose) synthetase activity in nuclei of dividing and of non-dividing but differentiating intestinal epithelial cells.
Poly(ADP-ribose) synthetase activity is found in nuclei of regenerating epithelial cells in the lower half of the crypts of guinea-pig small intestine. Nuclei from non-dividing but differentiating and maturing cells in the upper crypts and on the villi contain no more than about 10% of the synthetase activity of lower-crypt cell nuclei. The product in the active nuclei is shown to be 80% poly(ADP-ribosylated) protein and 20% mono(ADP-ribosylated) protein; 60% of thetotal labelled product was attached to acid-soluble proteins (including histones), and 40% to acid-insoluble (non-histone) proteins. The average number of ADP-ribosyl units in the oligomeric chains of the poly(ADP-ribosylated) proteins was 15 but the range of sizes of (ADP-ribose) oligomers attached to nuclear proteins was smaller in villus than in crypt cell nuclei.
ADP Ribose Transferases↗