Text

theses

Bacterial flagella are complex macro-molecular machines consisting of more than thirty different proteins. The bulk of the flagellum functions in the cell exterior. Therefore, the flagellar component proteins have to be exported during its biosynthesis. Bacteria develop flagella specific type III export pathways for the delivery of flagellar proteins outside the cytoplasm. The flagellar proteins are synthesized in the cytosol and are translocated through the central flagellar channel via a dedicated export apparatus to the distal growing end for the construction of the flagellum. The inner-membrane associated ATPase of flagellar export apparatus, FliI, is considered to be one of the central components in the export process. FliI is a Walker-type ATPase and functions as a hexamer. FliT is the flagellar export chaperone for the flagellar cap-forming protein FliD. It prevents premature aggregation of FliD in the cytosol and facilitates the export of FliD through the export channel. The interaction between FliT and FliI is crucial for the transport of FliD. We have studied the interaction between FliI and FliT using solution NMR combined with other biophysical techniques. Our biophysical data show that FliT interacts with the extreme N-terminal residues of FliI. FliT inhibits the enzymatic activity of FliI by disrupting FliI dimer. FliT is the only flagellar export chaperone known to inhibit the ATPase activity of FliI. We have determined the solution structure of FliI-FliT complex that provides the first high-resolution structure of any chaperone-ATPase complex of flagellar type III export pathway or type III secretion system in general. We have found that FliI binds to the hydrophobic cleft of FliT and the extreme N-terminal residues of FliI forms a α-helix upon FliT binding. The solution structure of FliI-FliT complex provides structural insight about possible binding interface of FliT with its substrate, FliD. Our NMR data as well as biochemical and bio-informative studies show that FliT might have common binding motif for its cognate substrate, FliD and the ATPase, FliI.

ETD_6094

Ph.D.

Includes bibliographical references

by Nandish Kumar Khanra

doi:10.7282/T3WS8W0W

ETD doctoral

The author owns the copyright to this work.