Petrovic, Arsen; (2004) Investigation of higher-order self-assembly of the DNA binding protein H-NS. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

H-NS, a DNA binding protein widely distributed in Gram-negative bacteria, acts as a global transcriptional regulator for the expression of a large number of genes. The 136 residue protein has a modular organisation with two structurally independent domains responsible for DNA binding and protein-protein interactions, respectively. Self-association of the H-NS polypeptide is intimately linked to the formation of a specific nucleoprotein structure capable of inhibiting transcription. Attempts at deciphering the structure/function relationship of the H-NS polypeptide have highlighted the convoluted relationship between the various regions in the primary sequence. A combination of complementary techniques was used to investigate self-assembly of the Salmonella typhimurium H-NS polypeptide. The results thus obtained suggest a possible model for the H-NS oligomerisation and highlight the importance of secondary structure in mediating a higher-order structure formation. The assembly of H-NS oligomers occurs through the association of the dimeric intermediate via two protein interfaces. The initial dimer formation occurs through the coiled-coil motif residing in the amino terminal domain (residues 1-49). The dimers thus formed associate in a head-to-tail fashion through the region encompassing residues 64-89 and 1-20. Mutagenesis studies underline the importance of the short amino-terminal helix H2 in supporting the higher-order oligomer formation. Hydrodynamic and modelling studies of the H-NS homologue, StpA, are also presented.

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