Further studies on the soluble form (gs) of rabies virus glycoprotein (g): molecular structure of gs protein and possible mechanism of the shedding.
In this study, we investigated the antigenic structures and maturation of some C-terminal-deficient derivatives of rabies virus glycoprotein (G). The Gs protein, a soluble form of G protein shed from infected cells, displayed antigenicity to most of our conformational epitope-specific anti-G mAbs, but took the 1-30-44 epitope-deficient conformation (termed G(C) form). (The 1-30-44 epitope was acid-sensitive and dependent on two separate regions, the Lys-202-containing and Asn-336-containing regions; Kankanamge et al., Microbiol. Immunol., 47: 507-519). Intact G proteins took the 1-30-44 epitope-positive form (referred to as G(B) form) on the cell surface, but not inside the cell. A deletion mutant G(1-429) (termed GDeltaTC), lacking the transmembrane (TM) and cytoplasmic domains, was shown to be accumulated in the rough endoplasmic reticulum (rER) with BiP and did not seem to be shed. Another C-terminal-deficient mutant G(1-462) (termed CT1) was deprived of the whole cytoplasmic domain except for a basic amino acid left at the C-terminus, but was transported to the cell surface, where it showed pH-dependent cell fusion activity and almost full antigenicity to most of the anti-G mAbs with the exception of very weak antigenicity to mAb #1-30-44. No Gs protein could be detected in the CT1-producing cultures. Based on these results, we think that the cytoplasmic domain was not necessary for the G protein to be transported to the cell surface, but was necessary to keep its 1-30-44 epitope-positive G(B) conformation. Gs proteins might have lost the C-terminal regions during the maturation process after being exported from the rER.
Thirapanmethee
Krit
K
Department of Molecular Microbiology, Graduate School of Pharmaceutical Sciences, Kyoto University.
Ootaki
Naohiro
N
Sakai
Mai
M
Lien
Chah Keng
CK
Kawai
Akihiko
A
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000914:Antibodies, Viral / Q000276:immunology; D000956:Antigens, Viral / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000502:physiology; D002460:Cell Line; D000939:Epitopes / Q000276:immunology*; D005455:Fluorescent Antibody Technique; D006023:Glycoproteins / Q000737:chemistry* / Q000276:immunology / Q000502:physiology; D011487:Protein Conformation; D017510:Protein Folding; D011820:Rabies virus / Q000276:immunology*; D012995:Solubility; D014759:Viral Envelope Proteins / Q000737:chemistry* / Q000276:immunology / Q000502:physiology; D017201:Virus Shedding / Q000502:physiology*
D000911:Antibodies, Monoclonal; D000914:Antibodies, Viral; D000956:Antigens, Viral; D000939:Epitopes; D006023:Glycoproteins; D014759:Viral Envelope Proteins; C064951:glycoprotein G, Rabies virus