Truncation of the COOH-terminal region of the paramyxovirus SV5 fusion protein leads to hemifusion but not complete fusion.

Abstract

The role of the simian virus 5 (SV5) fusion (F) protein 20 residue COOH- terminal region, thought to represent the cytoplasmic tail, in fusion activity was examined by constructing a series of COOH-terminal truncation mutants. When the altered F proteins were expressed in eukaryotic cells, by using the vaccinia virus-T7 transient expression system, all the F proteins exhibited similar intracellular transport properties and all were expressed abundantly on the cell surface. Quantitative and qualitative cell fusion assays indicated that all of the F protein COOH-terminal truncation mutants mediated lipid mixing with similar kinetics and efficiency as that of wild-type F protein. However, the cytoplasmic content mixing activity decreased in parallel with the extent of the deletion in the F protein COOH-terminal truncation mutants. These data indicate that it is possible to separate the presumptive early step in the fusion reaction, hemifusion, and the final stage of fusion, content mixing, and that the presence of the F protein COOH-terminal region is important for the final steps of fusion.

Roles for the Cytoplasmic Tails of the Fusion and Hemagglutinin-Neuraminidase Proteins in Budding of the Paramyxovirus Simian Virus 5

“…It was not possible to test accurately the fusion capacity of the F⌬20 protein in rSV5 F⌬20-infected cells as the level of surface expression of F⌬20 protein was always less than expression of wt F protein (data not shown), which would lead to an under-representation of the true amount of virus-mediated fusion. These data extend our earlier experiments using transient expression of F proteins with altered cytoplasmic tails (2) by showing that the extent of cell-cell fusion in virusinfected cells is not affected by truncations to the cytoplasmic tail of the F protein.…”

“…The diffuse migration pattern of the F⌬18 and F⌬20 proteins is presumably due to an altered carbohydrate modification. We observed previously that for a transiently expressed F protein lacking 19 residues of the cytoplasmic tail (F⌬19) that F⌬19 was modified by the addition of polylactosaminoglycan (2).…”

Polybasic KKR Motif in the Cytoplasmic Tail of Nipah Virus Fusion Protein Modulates Membrane Fusion by Inside-Out Signaling

“…The CTs of other paramyxovirus fusion proteins are known to be required for various protein functions, including proper surface expression, membrane fusion, fusion pore enlargement, transition from hemifusion to complete fusion, and/or budding (7,19,59,65,68), although removal of the CT has resulted in quite distinct phenotypes in different paramyxoviruses, ranging from no effect (12) to fusion pore formation (65) to fusion pore enlargement (19) to syncytium formation (59,65). In this report, we show that relatively large deletions in the NiV-F CT did not significantly compromise conformational integrity or CSE but can either reduce or enhance fusion (Fig.…”

Amino Acid Sequence Requirements of the Transmembrane and Cytoplasmic Domains of Influenza Virus Hemagglutinin for Viable Membrane Fusion

“…Although the CT is not required for HA-mediated fusion in influenza, for some other viruses its presence is known to be essential (Bagai et al, 1996). For many viruses, including influenza (Ohuchi et al, 1998), altering the fusion protein's CT can strongly affect fusion (Chakrabarti et al, 1989;Mulligan et al, 1992;Johnson et al, 1993;Ritter et al, 1993;Owens et al, 1994;Spies and Compans, 1994;Sergel and Morrison, 1995).…”