Intracellular processing of the Newcastle disease virus fusion glycoprotein

Abstract

The fusion glycoprotein (Fo) of Newcastle disease virus is cleaved at an intracellular site (Nagai et al., Virology 69:523-538, 1976) into F1 and F2. This result was confirmed by comparing the transit time of the fusion protein to the cell surface with the time course of cleavage of Fo. The time required for cleavage of half of the pulse-labeled Fo protein is ca. 40 min faster than the half time of the transit of the fusion protein to the cell surface. To determine the cell compartment in which cleavage occurs, use was made of inhibitors which block glycoprotein migration at specific points and posttranslational modifications known to occur in specific cell membranes. Cleavage of Fo is inhibited by carbonyl cyanide m-chlorophenylhydrazone; thus, cleavage does not occur in the rough endoplasmic reticulum. Monensin blocks the incorporation of Newcastle disease virus glycoproteins into virions and blocks the cleavage of the fusion glycoprotein. However, Fo cannot be radioactively labeled with [3H] fucose, whereas F1 is readily labeled. These results argue that cleavage occurs in the trans Golgi membranes or in a cell compartment occupied by glycoproteins quite soon after their transit through the trans Golgi membranes. The implications of the results presented for the transit times of the fusion protein between subcellular organelles are discussed.

Inhibition of the assembly of Newcastle disease virus by monensin

“…The inhibition of proteolytic cleavage of virulent NDV F, by monensin suggests that the enzyme for the cleavage of BHK cells is present somewhere after the monensin-sensitive step in the course of viral glycoprotein transport. This result is compatible with that of Morrison et al (1985) showing a similar intracellular localization of the proteolytic enzyme for NDV F,, in chick embryo cells.…”

“…In addition, the intracellular proteolytic cleavage, which is a phenomenon characteristic of virulent strains of NDV (Nagai et al, 1976b). was reported to be blocked by monensin (Morrison et al, 1985). We have confirmed these results in BHK cells.…”

“…Effect of monensin on the posttranslational processing of NDV g!c'coproteins in BHK cells Morrison et al (1985) have recently shown that monensin blocks the transport of NDV glycoproteins from the cis to the tram Golgi membranes of chick embryo cells. In addition, the intracellular proteolytic cleavage, which is a phenomenon characteristic of virulent strains of NDV (Nagai et al, 1976b).…”

Post-translational processing of the glycoproteins of lymphocytic choriomeningitis virus

“…Infected BHK monolayers also incubated in TUN were permeabilized with acetone, then stained to visualize intracellular GP-C (C). F proteins are cleaved in the trans-Golgi or the immediate trans-Golgi compartment (Sato et a/., 1988;Yamada et a/., 1988;Morrison et a/., 1985;Nagai et a/., 1976). However, for measles virus, unlike LCMV, cleavage apparently continues at the cell surface (Yamada et al, 1988).…”

Domains of Virus Glycoproteins

“…The actual cleavage sequence contains dibasic amino acids, which are sites for limited proteolysis in a wide variety of proteins including other enveloped virus glycoproteins, peptide hormones, and neuropeptide precursors. The proteolytic activity is localized to a trans-Golgi vesicle (Morrison et al, 1985) and is possibly the calcium-activated, thiol-type protease described by Steiner et al (1984).…”