Human cytomegalovirus open reading frame UL11 encodes a highly polymorphic protein expressed on the infected cell surface

Abstract

Human cytomegalovirus (HCMV) open reading frame (ORF) UL11 locates within a polymorphic region of the viral genome identified previously by a restriction-fragment-length-polymorphism. We report here that ORF UL11 encodes a polymorphic protein expressed on the surface of HCMV-infected cells. First, we determined the nucleotide sequence of ORF UL11 from ten strains and compared it among the strains. Out of 205 amino acids consisting of the predicted N-terminal region beside the putative transmembrane stretch in strain AD169, 88 residues were divergent on more than one strain. In contrast, the predicted C-terminal side including the putative transmembrane domain was identical at the amino acid sequence level. In addition, the number and location of predicted cysteine residues were also conserved. Next, we screened a cDNA library from HCMV-infected cells and obtained a cDNA clone containing the full-length ORF UL11. Finally, we identified the gene product of UL11 on the surface of HCMV-infected cells by FACS analysis with polyclonal antibodies generated against a glutathione S-transferase/UL11 fusion protein. The fusion protein contained a region within the N-terminal side next to the predicted transmembrane stretch. These results indicate that the N-terminal side of UL11 protein containing variable amino acid residues protrudes from the infected cell surface.

Expression of the Human Cytomegalovirus UL11 Glycoprotein in Viral Infection and Evaluation of Its Effect on Virus-Specific CD8 T Cells

“…In fact, previous reports (26,34) suggested that UL11 is present at the cell surface. To examine which forms of the UL11 protein are expressed at the plasma membrane, we performed biotinylation of cell surface proteins of CMV-infected cells and analyzed the protein fraction precipitated with streptavidin-coated beads by immunoblotting.…”

“…Upon higher separation of the proteins, it became apparent that the ϳ50-kDa bands are indeed represented by two forms (data not shown), which also pointed to further modification and is consistent with the occurrence of the two low-molecular-mass bands seen for the endo H-or PNGase Ftreated samples. The UL11 amino acid sequence contains a large threonine-rich stretch, which is a predicted substrate for O-glycosylation (26). Following treatment of the samples with O-glycosidase, there was no apparent change in the mobility of the different bands ( Fig.…”

“…Most intriguingly, the RL11 proteins share an immunoglobulinlike domain, termed RL11D, which was proposed to be structurally related to a similar domain present within the known immunomodulatory E3 proteins of adenoviruses (24). Interestingly, several of the RL11 proteins display remarkable amino acid polymorphism between different clinical isolates (2,24,26,27), implying that during evolution they were under diversifying selection pressure, possibly imposed by immune mechanisms and their polymorphic effector molecules. Some of the RL11 genes have been connected with immunomodulatory functions.…”

“…UL11 was the first CMV gene for which a high interstrain variability has been reported (26). In a recent study, our group characterized the UL11 protein by expressing it independently of CMV infection (34).…”

The Genes Encoding the gCIII Complex of Human Cytomegalovirus Exist in Highly Diverse Combinations in Clinical Isolates

“…Based on sequence analysis of gH from clinical isolates, which revealed variability at the N terminus, two major variants can be defined for the gH gene. Differences among strains have also been reported for UL11 (17), UL144 (30), and exon 3 of the immediate-early gene (15,54).…”