-p53-rasmol-study

🧬 Effect of Point Mutations on Protein Structure Stability

A RasMol-based Study

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📌 Overview

This project investigates the structural consequences of point mutations in the p53 tumor suppressor protein using RasMol, a molecular graphics visualization tool. By comparing the wild-type and mutant (R273H) forms of p53, the study demonstrates how even a single amino acid substitution can significantly disrupt protein conformation and impair biological function.

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🎯 Objectives

• To understand how point mutations alter protein 3D structure
• To visualize structural differences between wild-type and mutant p53 using RasMol
• To analyze the functional consequences of the R273H mutation
• To demonstrate the utility of RasMol for educational structural bioinformatics

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🦠 Protein of Interest: p53 Tumor Suppressor

Property	Details
Protein	p53 Tumor Suppressor
Wild-type PDB ID	1TUP – Human p53 bound to DNA
Mutant PDB ID	2OCJ – p53 with R273H point mutation
Mutation	Arginine (R) → Histidine (H) at position 273
Significance	One of the most common mutations in human cancers

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🛠️ Tools & Software

Tool	Version	Purpose
RasMol	v2.7.5	3D visualization and structural comparison
RCSB Protein Data Bank	—	Source for .pdb structure files
Notepad++	—	Writing and editing RasMol scripts
MS Paint / Photoshop	—	Annotating and labeling screenshots

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📁 Repository Structure

p53-rasmol-study/
│
├── README.md                   # Project overview (this file)
│
├── data/                       # PDB structure files
│   ├── 1TUP.pdb                # Wild-type p53
│   └── 2OCJ.pdb                # Mutant p53 (R273H)
│
├── scripts/                    # RasMol command scripts
│   ├── wildtype_visualization.rasmol
│   ├── mutant_visualization.rasmol
│   └── comparison_commands.rasmol
│
├── results/                    # Output images and analysis
│   ├── wildtype_p53.jpg        # RasMol screenshot - wild-type
│   ├── mutant_p53.jpg          # RasMol screenshot - mutant
│   └── structural_comparison.md
│
└── images/                     # Figures and diagrams

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🔬 Methodology

1. Protein Selection

Both wild-type (1TUP) and mutant (2OCJ) p53 structures were downloaded from the RCSB Protein Data Bank in .pdb format.

2. Visualization Pipeline

# Load wild-type structure
load 1TUP.pdb

# Render secondary structures
cartoons

# Highlight alpha helices in red
select helix; color red

# Highlight beta sheets in yellow
select sheet; color yellow

# Zoom for close-up view
zoom 150

# Export visualization
write image.jpg

3. Structural Observations

• Mutation site location and environment assessed visually
• Alpha helices and beta sheets compared for presence/integrity
• Surface accessibility and residue exposure changes noted
• Screenshots taken for side-by-side comparison

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📊 Key Results

Structural Feature Comparison

Structural Feature	Wild-type p53 (1TUP)	Mutant p53 R273H (2OCJ)
Alpha Helices	Seven well-formed helices, stable	Partial unravelling near residue 273
Beta Sheets	Tightly aligned, no gaps	Slight misalignment; less compact
Residue at 273	Arginine — small, hydrophilic, buried	Histidine — bulkier, hydrophobic, exposed
Surface Accessibility	Position 273 shielded from solvent	Noticeably greater solvent exposure
Hydrogen Bond Network	Intact; anchors DNA-binding loop firmly	Several bonds broken; loop destabilised
DNA Binding Capacity	Fully functional	Severely impaired

Key Finding

The R273H mutation introduces a bulkier, more hydrophobic histidine in place of the small, hydrophilic arginine. This disrupts the local hydrogen bond network, increases surface exposure, and impairs the protein's ability to bind DNA — ultimately leading to loss of tumor-suppressing function.

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🖼️ Figures

Figure 1: Wild-type p53 highlighting the R273 residue (red) within the DNA-binding surface.

Figure 2: Mutant p53 structure with H273 showing outward orientation and solvent exposure.

(See /results/ folder for full-resolution RasMol screenshots)

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⚠️ Limitations

While RasMol provides valuable qualitative insights, it lacks:

• Simulation of protein flexibility or motion over time
• Quantification of energetic penalties due to mutation
• Visualization of interaction dynamics with DNA or ligands

Future work could incorporate tools like GROMACS (molecular dynamics) or PyMOL / Swiss-Model for quantitative and dynamic analysis.

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📖 Conclusion

This study demonstrates that even a single amino acid change (R273H) can significantly alter protein conformation in functionally critical regions such as the DNA-binding domain of p53. The findings align with established literature on loss-of-function p53 mutations in cancer, and reinforce the value of computational visualization in structural biology education.

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📚 References

1. Cho, Y. et al. (1994). Crystal structure of a p53 tumor suppressor-DNA complex. Science, 265(5170), 346–355.
2. Joerger, A. C., & Fersht, A. R. (2008). Structural Biology of the Tumor Suppressor p53. Annual Review of Biochemistry, 77, 557–579.
3. Berman, H. M. et al. (2000). The Protein Data Bank. Nucleic Acids Research, 28(1), 235–242.
4. Sayle, R. A., & Milner-White, E. J. (1995). RasMol: Biomolecular graphics for all. Trends in Biochemical Sciences, 20(9), 374–376.
5. Petsko, G. A., & Ringe, D. (2004). Protein Structure and Function. New Science Press.

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👩‍🔬 Author

Archa S