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A novel intermediate in processing of murine leukemia virus envelope glycoproteins. Proteolytic cleavage in the late
1Department of Pathology, University of Southern California Health Sciences Center, Los Angeles 90033.
Abstract:
The intracellular processing of the murine leukemia virus envelope glycoprotein precursor Pr85 to the mature products gp70 and p15e was analyzed in the mouse T-lymphoma cell line W7MG1. Kinetic (pulse-chase) analysis of synthesis and processing, coupled with endoglycosidase (endo H) and neuraminidase digestions revealed the existence of a novel high molecular weight processing intermediate, gp95, containing endo H-resistant terminally glycosylated oligosaccharide chains. In contrast to previously published conclusions, our data indicate that proteolytic cleavage of the envelope precursor occurs after the acquisition of endo H-resistant chains and terminal glycosylation and thus after the mannosidase II step. In the same W7MG1 cell line, the type and order of murine leukemia virus envelope protein processing events was identical to that for the mouse mammary tumor virus envelope protein. Interestingly, complete mouse mammary tumor virus envelope protein processing requires the addition of glucocorticoid hormone, whereas murine leukemia virus envelope protein processing occurs constitutively in these W7MG1 cells. We propose that all retroviral envelope proteins share a common processing pathway in which proteolytic processing is a late event that follows acquisition of endo H resistance and terminal glycosylation.
Insights
Murine leukemia virus envelope glycoprotein processing involves a novel gp95 intermediate. Proteolytic cleavage occurs late, after acquiring endo H-resistant chains and terminal glycosylation.
Area of Science:
- Retroviral protein processing
- Molecular biology
- Cellular glycosylation
Background:
- Understanding retroviral envelope glycoprotein processing is crucial for virology.
- Previous studies suggested different processing pathways for murine leukemia virus (MuLV).
Purpose of the Study:
- To analyze the intracellular processing of MuLV envelope glycoprotein precursor Pr85.
- To identify and characterize processing intermediates and the order of events.
Main Methods:
- Kinetic (pulse-chase) analysis of protein synthesis and processing.
- Endoglycosidase (endo H) and neuraminidase digestions to analyze oligosaccharide chains.
- Analysis in the W7MG1 mouse T-lymphoma cell line.
Main Results:
- Identified a novel high molecular weight intermediate, gp95.
- gp95 contains endo H-resistant, terminally glycosylated oligosaccharide chains.
- Proteolytic cleavage occurs late in processing, after endo H resistance and terminal glycosylation acquisition, contrary to prior conclusions.
- MuLV and mouse mammary tumor virus (MMTV) envelope protein processing pathways are similar in W7MG1 cells.
Conclusions:
- Retroviral envelope proteins likely share a common processing pathway.
- Proteolytic processing is a late event, following acquisition of endo H resistance and terminal glycosylation.
- MuLV processing is constitutive, while MMTV processing requires glucocorticoid hormone.