Abstract
The shell of a virus is composed by protein and intends to protect the DNA in the virus. The DNA will release from viral capsid by internal pressure when virus attaches the cytoplasm. The structure of capsid is well known from scanning-force microscopy (SFM) or cryo-EM studies. Bacteriophage Phi-29 can package double-stranded DNA with the length of 6.6 um into a capsid. When packaged, the DNA is kept under high pressure (about 6MPa) inside the viral shell. Therefore, the bacteriophage capsid serves as a high-pressure container. Ivanovska placed the nano tip of an atomic force microscope (AFM) onto the shell of a bacteriophage, increased the force applied by the tip slowly and recorded the deformation of the shell. The result shows that empty shells withstand nanonewton forces while being indented up to 30% of their height. By combining with simulation and theoretical method, the Young's modulus of bacteriophage shell is 1.8GPa in empty. In this research, by using the analytical solution (method 1, method 2) and finite element method that include three approaches were proposed to find the stress in the nanoshell when phi-29 packages the dsDNA. Method 1 is assumed that the capsid is simplified as a hollow sphere loaded by an inner pressure of 6 MPa and its outer pressure is 0 MPa. From analytical solution the stress in the capsid is 47.6 MPa. When it comes to method 2, the capsid is assumed to be a cylindrical vessel with ellipsoidal heads and loaded by an inner pressure, 6MPa. The stress in the capsid calculated from method 2 is 83.4 MPa. To method 3, the analysis software is applied to simulate the true-structure-like phi-29 capsid mode. From the simulation result, the stress in the capsid shell is 116.6 MPa. The results of the numerical simulation show the best agreement to the experimental data among these three methods. The method proposed here would be used to study the mechanical behavior in DNA packaging and release from viral capsids in the future.