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Interstrain variation of the major internal structural component (p30gag) of two murine oncornaviruses: comparative
Abstract:
The major internal structural protein (p30(gag)) of the Moloney leukemia virus and the endogenous Y-1 murine oncornavirus was examined for biochemical and biophysical manifestations of interstrain antigenic variation. Although the two viral proteins share murine group-specific antigenic determinants, the Y-1 virus p30 appeared to have both a lower relative number of such determinants and a decreased affinity at the cross-reactive sites for Moloney virus p30 monospecific antibodies. Further, immunological analysis indicated the presence of unique antigenic sites on the Moloney virus p30 not shared by the analogous Y-1 virus molecule. The two polypeptides copurified and had similar isoelectric points (pH 6.2 to 6.3) and sedimentation coefficients (2.47S). However, equilibrium sedimentation yielded a significant mass difference between the two proteins, 28,300 +/- 600 and 31,000 +/- 300 daltons for the Moloney and Y-1 virus molecules, respectively. Amino acid analysis indicated a concomitant increase in total residues for the Y-1 virus p30, although a number of residues appeared to have been conserved between the two viral proteins. Conformational studies and hydrodynamic calculations demonstrated marked secondary and tertiary structural differences; with the Y-1 virus p30 being an asymmetric prolate ellipsoid containing 27 to 28% alpha-helix and Moloney virus p30 being somewhat more spherical and possessing an alpha-helical content of 50 to 55%. Two-dimensional mapping of (125)I-labeled tryptic peptides of each p30 suggested that considerable sequence heterogeneity is responsible for many of the biophysical, biochemical, and immunochemical differences in these two analogous structural proteins.
Insights
Structural proteins (p30(gag)) from Moloney leukemia virus and Y-1 murine oncornavirus show significant antigenic variation. Differences in antigenic sites and structure contribute to interstrain variation in these retroviral proteins.
Area of Science:
- Virology
- Structural Biology
- Immunology
Background:
- Murine oncornaviruses, including Moloney leukemia virus and endogenous Y-1 virus, possess a major internal structural protein p30(gag).
- Understanding interstrain antigenic variation in viral proteins is crucial for viral classification and vaccine development.
Purpose of the Study:
- To investigate the biochemical and biophysical basis of interstrain antigenic variation in the p30(gag) proteins of Moloney leukemia virus and Y-1 murine oncornavirus.
- To compare the antigenic determinants, molecular mass, amino acid composition, and structural conformation of these two viral proteins.
Main Methods:
- Immunological analysis using monospecific antibodies.
- Equilibrium sedimentation to determine molecular mass.
- Amino acid analysis.
- Conformational studies and hydrodynamic calculations.
- Two-dimensional mapping of tryptic peptides.
Main Results:
- Both p30(gag) proteins share group-specific antigenic determinants but differ in the number and affinity of these sites.
- Moloney virus p30 possesses unique antigenic sites absent in Y-1 virus p30.
- Significant differences in molecular mass (28,300 Da for Moloney vs. 31,000 Da for Y-1) and secondary/tertiary structure were observed.
- Y-1 virus p30 is more asymmetric with lower alpha-helical content (27-28%) compared to the more spherical Moloney virus p30 (50-55% alpha-helix).
- Tryptic peptide mapping revealed considerable sequence heterogeneity between the two proteins.
Conclusions:
- Interstrain antigenic variation in p30(gag) proteins is driven by differences in amino acid sequence.
- These sequence variations lead to distinct biochemical, biophysical, and immunochemical properties, including antigenic site composition and protein conformation.
- The findings highlight the structural plasticity of retroviral proteins and its implications for viral evolution and immunology.