Role of partial proteolysis in processing murine leukemia virus membrane envelope glycoproteins to the cell surface. A viral mutant with uncleaved glycoprotein.

C A Machida,D Kabat

doi:10.1016/s0021-9258(19)45336-2

Abstract

We have isolated a mutant Rauscher murine leukemia virus (R-MuLV) with a mutation in its envelope (env) glycoprotein gene. This mutant encodes a membrane glycoprotein with an apparent Mr = 80,000 (gPr80env) that contains both gp70 and p15E antigenic determinants found in the larger wild type R-MuLV env precursor molecule gPr90env. Glycosylation inhibition and peptide mapping analyses indicate that the smaller size of the mutant glycoprotein is caused by a shortening of its polypeptide chain rather than by reduced glycosylation. Unlike gPr90env of wild type R-MuLV which contains Asn-linked high mannose oligosaccharides and is processed by partial proteolysis and by further glycosylation in the Golgi apparatus to produce gp70 plus p15E, the mutant glycoprotein can reach the cell surface without proteolysis. The uncleaved plasma membrane component, which undergoes further glycosylation during its transit through the Golgi apparatus, has an apparent Mr = 85,000. Furthermore, this cell surface glycoprotein is incorporated into released virions which are infectious. However, the mutant envelope glycoproteins on the cell surface do not block the receptors needed for superinfection by wild type MuLV. These results indicate that transport of uncleaved env gene-encoded glycoproteins to the cell surface is not a unique attribute to leukemia-producing recombinant of dual tropic MuLVs (Famulari, N. G., and English, J. K. (1981) J. Virol. 40, 971-976) but can also occur with a mutant of ecotropic MuLV.

Highlights

We have isolated a mutant Rauscher murineleuke- the latter sugars occurs during glycoprotein transit through mia virus (R-MuLV) with a mutation in its envelope the Golgi apparatusenroutetothe cell surface [1, 5, 6]
Glycosylation inhibition and peptide mappinganalyses indicate that the smaller size of the mutant glycoproteinis caused by a shortening of its polypeptidechainratherthan by reduced glycosylation.Unlike gPr90'""of wild type R-MuLV which contains Asn-linkedhigh mannose oligosaccharidesand is processed by partial proteolysis andby
The mutanetn- suggesting that the abnormal enu gene products on the cell velope glycoproteins on the cell surface do not block surface do not cause complevtieral interference.These results the receptors needed for superinfection by wild type support theidea that different regionsof gp7Operform distinct

Summary

A VIRAL MUTANT WITH UNCLEAVED GLYCOPROTEIN*

From the Departmentof Biochemistry, School of Medicine, Oregon Health Sciences Uniuersity, Portland, Oregon 97201. The uncleaved plasma This paper describesa mutant of Rauscher MuLV that membranecomponent,whichundergoesfurther gly- encodesa slightly smaller enu precursor molecule thatis cosylation during its transit through the Golgi appa- transferred to thcell surface and is incorporated intoinfective ratus, has an apparent M , = 85,000.

EXPERIMENTAL PROCEDURES

The abbreviations used are

RESULTS

DISCUSSION