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Nearest-neighbor interactions of the major RNA tumor virus glycoprotein on murine cell surfaces
Abstract:
Formaldehyde-fixed Staphylococcus aureus and monospecific antiserum to gp70, the major envelope glycoprotein of murine leukemia virus, were used to immunoadsorb gp70 from Nonidet P40 extracts prepared from surface-radioiodinated murine cells. The labeled gp70 molecules in these cells were linked to a protein of approximately 15,000 daltons via native disulfide bonding. Prior treatment of cells with the reversible, bifunctional, crosslinking reagent dimethyl-3,3'-dithiobispropionimidate, followed by immunoadsorption and two-dimensional diagonal electrophoresis, revealed apparent homodimers and homotrimers of the 85,000-dalton complex. Identical treatment of purified type C RNA tumor virus from murine cells also revealed homodimeric and homotrimeric species, demonstrating similar self-associating tendencies of this glycoprotein in both intact virus and the plasma membrane of nonproducing murine cells. One cross-linked product consistently detected on the surfaces of murine cells was not present after crosslinking of a representative strain of murine leukemia virus.
Insights
Murine leukemia virus gp70 glycoprotein forms dimers and trimers on cell surfaces and in viruses. This self-association tendency is similar in both intact virus and plasma membranes of murine cells.
Area of Science:
- Biochemistry
- Virology
- Cell Biology
Background:
- The major envelope glycoprotein of murine leukemia virus, gp70, is crucial for viral structure and function.
- Understanding the self-associating properties of gp70 is important for studying viral assembly and cell-surface interactions.
Purpose of the Study:
- To investigate the self-associating tendencies of the gp70 glycoprotein on the surface of murine cells.
- To compare the oligomeric state of gp70 in intact murine leukemia virus with that on the plasma membrane.
Main Methods:
- Surface radioiodination of murine cells followed by Nonidet P40 extraction.
- Immunoadsorption of gp70 using specific antiserum and formaldehyde-fixed Staphylococcus aureus.
- Crosslinking of surface proteins using dimethyl-3,3'-dithiobispropionimidate.
- Analysis of cross-linked products by two-dimensional diagonal electrophoresis.
Main Results:
- gp70 molecules on murine cells were found to be linked to a 15,000-dalton protein via disulfide bonds.
- Two-dimensional diagonal electrophoresis revealed homodimers and homotrimers of an 85,000-dalton complex containing gp70.
- Purified murine leukemia virus also showed similar homodimeric and homotrimeric species of gp70.
- A specific cross-linked product found on murine cells was absent in the cross-linked virus.
Conclusions:
- The gp70 glycoprotein exhibits self-associating properties, forming dimers and trimers.
- These self-associating tendencies are conserved between gp70 on the plasma membrane of murine cells and in the intact murine leukemia virus.
- Differences in cross-linked products suggest potential variations in gp70 structure or interactions between cell-associated and free viral forms.