Date of Completion

5-13-2019

Embargo Period

5-11-2019

Keywords

Bacteriophage P22, capsid stability, stabilizing interactions, capsid assembly

Major Advisor

Dr. Carolyn Teschke

Associate Advisor

Dr. Joerg Graf

Associate Advisor

Dr. Daniel Gage

Associate Advisor

Dr. Spencer Nyholm

Associate Advisor

Dr. Victoria Robinson

Field of Study

Microbiology

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Bacteriophage P22 is an icosahedral phage with T=7 symmetry infecting host Salmonella enterica serovar Typhimurium. P22 is an ideal model system to understand the assembly mechanisms of other phages and viruses such as the Herpes Simplex Virus due to the presence of the HK97 fold in their coat proteins. The assembly mechanism is a well-orchestrated event; however, we are yet to comprehend the significant structural changes that proteins undergo during assembly. The end of the assembly process is marked by the formation of a procapsid which then undergoes numerous conformational changes to form a functional, infectious virion. This event is termed conformational switch. These changes provide the capsid which additional stability to withstand both the internal pressure during DNA packaging and the repulsive pressures while maintaining the DNA in the capsid shell. The phage capsid also needs to be able to endure the pressure from DNA ejection or release into the host cell.

Previously, the N-arm and P-domain were shown to interact during the conformational change to provide the capsid with stability (Parent et al., 2010b). The D-loops in the I-domains interact across the two-fold axes of symmetry using ionic interactions to act like a molecular staple (D'Lima and Teschke, 2015). The E-loop also undergoes movement during the conformational switch and has been shown to be important in stabilizing the capsids of other systems such as HK97, T4 and T7 bacteriophages(Fokine et al., 2006; Guo et al., 2014; Wikoff et al., 2000). This dissertation elucidates the role of E-loop in capsid stability and the various intracapsomer (between two adjacent coat monomeric subunits within the same capsomer) and intercapsomer (between two adjacent hexons or hexons and pentons) interactions that play a role in capsid stability. This is done by teasing apart a network of hydrophobic interactions between the E-loop and P-domains at intracapsomer and intercapsomer levels, acting like a hydrophobic brace holding the capsid together. This work shows the importance of these interactions in capsid assembly and thereby capsid stability of bacteriophage P22.

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