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Title: Structural studies of the TssA and TssK subunits from the type VL secretion system
Author: Dix, Samuel R.
ISNI:       0000 0004 7658 599X
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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The type VI secretion system (T6SS) is a protein assembly involved in the injection of effector proteins into target cells. The T6SS is critical for inter-bacterial competition, and also play a role in eukaryotic virulence. The T6SS assembly consists of a cell membrane complex to which a bacteriophage-like contractile tail is attached, mediated through a baseplate complex. Currently, very little information is known about the structural arrangement of the T6SS baseplate, in particular the components TssA and TssK. This thesis discusses the structural and complementary interaction studies carried out for both components from various bacterial orthologues. TssA has been classified into four sub-clades (TssA1A, TssA1B , TssA2A and TssA2B ). Subsequent structural studies have provided a model for the conserved ImpA_N region, found in the Nt1 domain of all TssA's. In addition, the structure for the CTD oligomer from a TssA1B representative (B. cenocepacia) and TssA2A representative (A. hydrophila) were determined, demonstrating the broad range of symmetry and mobility that can be exhibited by TssA. Further interaction studies indicate that despite the radically different symmetries displayed by the various TssA orthologue CTD oligomers, they maintain similar interactions with other T6SS subunits. The second component, TssK, has also been structurally characterised from both B. cenocepacia and B. pseudomallei. The X-ray structure of B. cenocepacia TssK indicates the subunits assemble as a trimer and are formed of three domains the shoulder, neck and head, displaying structural similarity with Lactococcal siphophage receptor binding proteins, consistent with E. coli TssK. In addition, interaction studies of B. cenocepacia TssK with other T6SS components suggests a similar pattern of interaction as E. coli TssK. Furthermore, structural comparisons of B. cenocepacia TssK with E. coli TssK identifies distinct differences in the orientation of the head domain, suggesting that mobility is an important feature in the role of TssK.
Supervisor: Rice, David W. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available