Determinants of retrovirus and alphavirus envelope protein processing and virion incorporation
Retroviruses pose significant health risks to humans and cause immunodeficiencies and leukemias in vertebrates. Moloney murine leukemia virus (Mo-MuLV) is an oncogenic retrovirus that replicates by reverse transcription. The virus infects a cell by receptor-mediated membrane fusion brought about by envelope glycoproteins. The glycoproteins are synthesized in the ER as a precursor that is cleaved by cellular endoproteases into two subunits, SU and TM. This cleavage is required for virus infectivity as it releases the amino-terminus of TM that contains a fusion peptide. The fusion peptide is instrumental in the membrane fusion process. Some studies have also suggested that the cleavage is required for envelope protein incorporation into virions, while others have suggested otherwise. Due to lack of a clear understanding for the requirement of cleavage, we have conducted a comprehensive biochemical study of the cleavage site. We have determined that this cleavage plays an important role in membrane fusion as well as the envelope protein incorporation into virions by affecting its intracellular transport. Alphaviruses are arthropod-borne RNA viruses that infect a broad range of vertebrates and invertebrates to cause encephalitis, arthritis, fever, rashes etc. The alphavirus Venezuelan equine encephalitis virus (VEEV) causes encephalitis in horses and humans, and has also been developed as a bio-weapon by some countries. The virus enters a susceptible cell by receptor-mediated endocytosis and low-pH mediated membrane fusion. The entry steps are initiated by the viral surface glycoproteins E2 and E1, which are arranged in heterotrimeric complexes called spikes. E2 is synthesized as a precursor PE2 that is cleaved into E3 and E2 by furin-like proteases. E3 is believed to stabilize the E2-E1 complex under low-pH conditions but the exact mechanism remains unknown. Here we have used retrovirus based pseudotypes of VEEV to determine the role of VEEV E3 in spike formation, incorporation into virions and virus infectivity by targeting the conserved regions of E3. We have determined that the cysteine residues and a glycosylation site located in E3 have important roles in the spike assembly. We have also attempted to study the structural aspects of E3.
Sanders, Purdue University.
Molecular biology|Cellular biology|Virology
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