Biological function of the low-pH, fusion-inactive conformation of rabies virus glycoprotein (G): G is transported in a fusion-inactive state-like conformation.
The glycoprotein (G) of rabies virus can assume at least three different conformations: the native (N) state detected at the viral surface above pH 7; the activated (A) hydrophobic state, which is probably involved in the first steps of the fusion process; and the fusion-inactive (I) conformation. There is a pH-dependent equilibrium between these states, the equilibrium being shifted towards the I state at low pH. It has been supposed that the transition from the N to the I state mediates membrane fusion. By using a lipid-mixing assay, we studied the kinetics of fusion and fusion inactivation for two rabies virus strains, PV and CVS. In addition, by using electron microscopy and a trypsin sensitivity assay, we analyzed the kinetics of the conformational change towards the I state for both strains. Although the PV strain fuses faster, inactivation and the conformational change of PV G occur more slowly than for the CVS strain. This suggests that the structural transition towards the I state is irrelevant to the fusion process. Immunofluorescence and immunoprecipitation experiments performed with infected cells and two different monoclonal antibodies, one specific for the N form of G and one which recognizes both the N and the I states, suggest that G is transported in an I state-like conformation through the Golgi apparatus and acquires its N structure only near or at the cell surface. We propose that the role of the I state is to avoid unspecific fusion during transport of G in the acidic Golgi vesicles.
Gaudin
Y
Y
Laboratoire de génétique des virus du CNRS, Gif sur Yvette, France.
Tuffereau
C
C
Durrer
P
P
Flamand
A
A
Ruigrok
R W
RW
D000818:Animals; D000911:Antibodies, Monoclonal; D000918:Antibody Specificity; D000956:Antigens, Viral; D001345:Autoradiography; D001692:Biological Transport; D002460:Cell Line; D006224:Cricetinae; D000939:Epitopes / Q000032:analysis; D005455:Fluorescent Antibody Technique; D006023:Glycoproteins / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007668:Kidney; D007700:Kinetics; D008081:Liposomes; D008561:Membrane Fusion; D008715:Methionine / Q000378:metabolism; D008854:Microscopy, Electron; D011487:Protein Conformation; D011820:Rabies virus / Q000502:physiology* / Q000648:ultrastructure; D013997:Time Factors; D014759:Viral Envelope Proteins / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D000956:Antigens, Viral; D000939:Epitopes; D006023:Glycoproteins; D008081:Liposomes; D014759:Viral Envelope Proteins; C064951:glycoprotein G, Rabies virus; D008715:Methionine