FliC or flagellin is the monomer subunit of the bacterial
flagella filament responsible for the motility of pathogenic bacteria such as Salmonella. The native form consists of 4 domains but
only D1 and D2 were modeled bound to TLR5. A D0 domain deletion variant of FliC
was used as it had almost no effect on binding affinity and simplifies the
crystallization. The D3 domain could not be modeled as it had extremely poor
electron density, most likely due to it being disordered when bound to TLR5.
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| Figure 2.1 Domains and secondary structure of FliC: The protein is colored as a rainbow from the N-terminus (blue) to the C-terminus (red) |
TLR5 only recognizes and binds the highly conservative D1
domain of FliC which consists of 4 regions: 2 N-terminal α-helices (αND1a and αND1b), 1 C-terminal α-helix (αCD1) and a β-hairpin segment. These secondary structures assemble into a rod shaped domain.
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| Figure 2.2 Protein-protein interaction interfaces of FliC |
FliC is involved in the formation of 3 different interfaces; the two primary
interfaces that TLR5 binds to form the 1:1 heterodimer (labelled green and
blue), as well as the secondary dimerization interface that TLR5’ binds to form
the 2:2 tetramer (labelled red).
The GIFs are great in helping to visualise where each domain interacts and the position of the interfaces, but the labels are a little difficult to read. Perhaps making them a little larger, or the GIFs move slower would help.
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