A unique glycoprotein containing GR-mouse mammary tumor virus peptides and additional peptides unrelated to viral
Abstract:
A glycoprotein of molecular weight 130,000 (gP130) has been precipitated from the cytoplasm of GR-strain mouse mammary tumor (GR-MMT) cells by a rabbit antiserum (anti-MMTV) to GR-strain mouse mammary tumor virus (GR-MMTV). This protein was not precipitated by antisera specific for detergent-disrupted C3H-strain MMTV (C3H-MMTV); C3H-MMTV glycoproteins; C3H-MMTV nonglycosylated proteins; GR-MMTV p25 or p12; RIII strain (milk) MMTV proteins; or Rauscher murine leukemia virus (R-MuLV) proteins; nor was it precipitated by normal rabbit serum. Two-dimensional thin layer analysis of 35S-methionine-containing tryptic peptides revealed that five of nine gp33 peptides and one of seven gp55 peptides are shared by gP130 and gPr76env. The envelope protein precursor, gPr76env, contains all of the gp33 peptides and six of seven gp55 peptides. One peptide in gPr76env, possibly a gp55-gp33 junction peptide, is also apparently present in gP130. Six of ten p25 peptides and four more gag-related peptides are shared by PR78gag and gP130. Protein gP130 also contains several tryptic peptides not found in gPr76env or in the core protein precursors Pr78gag, Pr110gag or Pr180gag-pol. Radioimmunoprecipitation experiments showed that gP130 could be precipitated from extracts of GR-MMTV cells with anti-MMTV serum even after antibodies to the known MMTV structural proteins had been removed from the serum by absorption. Both gP130 and a second protein, p30, were found in immunoprecipitates of detergent-disrupted isotopically labeled GR-MMTV treated with the absorbed anti-MMTV serum. These results suggest that antibodies to gP130 in the anti-MMTV serum are capable of recognizing those protein sequences unique to gP130; that is, those protein sequences which are not related to viral structural proteins. In light of these data and data published previously, gP130 is apparently a polyprotein containing juxtaposed components translated from the 5' and 3' end of the MMTV genome and protein components not previously identified as virus-specific.
Insights
Researchers identified a novel glycoprotein, gP130, in GR-strain mouse mammary tumor cells. This protein contains unique sequences not found in known mouse mammary tumor virus (MMTV) structural proteins, suggesting it
Area of Science:
- Virology
- Molecular Biology
- Oncology
Background:
- Mouse mammary tumor virus (MMTV) is a retrovirus associated with mammary tumors in mice.
- Understanding MMTV protein structure and function is crucial for studying viral pathogenesis and developing diagnostics or therapeutics.
- Previous studies have identified various MMTV structural proteins and their precursors.
Purpose of the Study:
- To characterize a novel glycoprotein, gP130, isolated from GR-strain mouse mammary tumor (GR-MMT) cells.
- To determine the relationship of gP130 to known MMTV structural proteins and their precursors.
- To investigate the potential for unique viral protein sequences within gP130.
Main Methods:
- Precipitation of gP130 from GR-MMT cell cytoplasm using rabbit antiserum (anti-MMTV) against GR-MMTV.
- Specificity testing of anti-MMTV serum against various MMTV strains and related viruses.
- Two-dimensional thin-layer analysis of tryptic peptides to compare gP130 with known MMTV proteins (gPr76env, PR78gag).
- Radioimmunoprecipitation experiments with absorbed anti-MMTV serum to identify unique gP130 epitopes.
Main Results:
- gP130 was specifically precipitated by anti-MMTV serum and not by antisera against other MMTV strains or Rauscher murine leukemia virus.
- Peptide analysis revealed shared peptides between gP130 and MMTV envelope precursor (gPr76env) and gag precursor (PR78gag), but also unique peptides in gP130.
- Radioimmunoprecipitation confirmed that antibodies to gP130 could recognize unique protein sequences not related to known MMTV structural proteins, even after absorption.
Conclusions:
- gP130 is a distinct glycoprotein found in GR-MMT cells.
- gP130 appears to be a polyprotein containing components from both the 5' and 3' ends of the MMTV genome.
- gP130 possesses unique protein sequences not previously identified as virus-specific, suggesting a novel viral component.
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