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Structural characterization of a 14-residue peptide ligand of the retinoblastoma protein: comparison with a
K Breese1, T Friedrich, T T Andersen
1Albany Medical College.
Abstract:
The retinoblastoma protein, a 110-kDa nuclear anti-oncoprotein, complexes specifically with transforming proteins of several oncogenic DNA viruses. A peptide [NLFCSEEMPSSDDE] derived from one of the viral proteins (simian virus 40 large T antigen) is known to competitively bind retinoblastoma protein, but a mutant analog [NLFCSKEMPSSDDE] does not. We studied the T peptide with HPLC to determine whether it can dimerize, and we employed circular dichroism spectroscopy to determine whether both peptides can exist in stable secondary structural conformations. HPLC analyses revealed that the T peptide is subject to oxidation and readily dimerizes. Circular dichroism analyses showed that both peptides can be induced to form stable secondary structural conformations under conditions that stabilize intramolecular hydrogen bonding in short peptides (90% 2,2,2-trifluoroethanol; 4 degrees C). The circular dichroism spectra of both peptide species were similar except for a statistically significant difference in the contour near 210 nm. Spectral analysis of the T-derived peptide species predicted elements of alpha-helix (18%), antiparallel beta-sheet (21%), beta-turn (22%) and unordered conformations (41%). An analysis of the mutant peptide species also predicted elements of alpha-helix (8%), antiparallel beta-sheet (28%), beta-turn (22%) and unordered conformations (40%). Thus, a small difference in the stabilized secondary structural conformations of the two sets of peptide species might partly explain their differential binding affinities for retinoblastoma protein, but it is likely that electrostatic charge differences resulting from the glutamic acid to lysine substitution play a dominant role.
Insights
Simian virus 40 T antigen peptides bind retinoblastoma protein. A mutation alters peptide structure and charge, impacting binding affinity, with charge differences playing a dominant role.
Area of Science:
- Molecular Biology
- Biochemistry
- Oncology
Background:
- Retinoblastoma protein is a nuclear anti-oncoprotein.
- It complexes with transforming proteins of oncogenic DNA viruses.
- Simian virus 40 (SV40) large T antigen is one such viral protein.
Purpose of the Study:
- To investigate the dimerization potential of an SV40 T antigen-derived peptide.
- To determine if this peptide and a mutant analog adopt stable secondary structures.
- To correlate structural differences with differential binding affinities to retinoblastoma protein.
Main Methods:
- High-performance liquid chromatography (HPLC) for peptide dimerization and oxidation analysis.
- Circular dichroism (CD) spectroscopy to assess secondary structural conformations.
- Peptide sequence analysis to predict structural elements.
Main Results:
- The T antigen peptide is prone to oxidation and dimerization.
- Both peptides can form stable secondary structures in 90% trifluoroethanol at 4°C.
- CD spectra showed minor differences, with predicted alpha-helix, beta-sheet, and beta-turn conformations varying slightly between peptides.
Conclusions:
- While subtle differences in secondary structure may contribute, electrostatic charge differences arising from a key amino acid substitution (glutamic acid to lysine) are likely the primary drivers of differential retinoblastoma protein binding.
- This finding has implications for understanding viral oncoprotein interactions and potential therapeutic strategies.