Did viruses enable sex?

Dengue virus E glycoproteins (monomer at top) lie flat on the virus particle as dimers (middle). At endosomal low pH, three monomers reorient to place the fusion peptide (orange) into the cell membrane. Image credit. A key step in sexual reproduction is the fusion of haploid cells to form a diploid zygote, yet the molecular mechanism underlying this joining of cells is poorly understood. Two studies reveal amazing similarities between proteins required for fusion of sperm and egg, and virus with host cells. A screen for genes that cause male sterility in the flowering plant Arabidopsis led to the identification of the HAP2 protein. This protein was later found to be important for sperm-egg fusion in Arabidopsis and in the unicellular algae Chlamyodomonas.  Homology modeling shows that the HAP2 protein looks very much like a class II viral fusion protein (illustrated). Found in dengue virus and many related viruses, dimers of these viral glycoproteins lie flat on the viral membrane, and are comprised largely of beta-strands. At one end of the protein is a fusion loop which allows the virus and cell membranes to join at the start of infection. The HAP2 protein also has what looks to be a viral fusion loop. Removal or alteration of this sequence in Tetrahymena prevents fusion of mating cells. The fusion loop of the dengue virus E glycoprotein cannot substitute for the HAP2 sequence. Furthermore, vesicular stomatitis viruses with HAP2 in place of the viral glycopr...
Source: virology blog - Category: Virology Authors: Tags: Basic virology Information Arabidopsis dengue virus fertilization fusion loop gamete glycoprotein HAP2 membrane fusion sperm-egg fusion type II fusion protein viral viruses Source Type: blogs