Molecular recognition of colicin U and Y pore-forming domains by their cognate immunity proteins.

Colicin U is an antibacterial pore-forming toxin produced by Shigella boydii that kills sensitive bacterial strains of Escherichia coli and closely related organisms [1]. The colicin U transmembrane immunity protein [2] that is encoded on the pColU plasmid ensures that producer bacteria are protected against the colicin U lethal action. The colicin-immunity protein recognition is a suitable model for studying protein-protein interactions. More than 40 mutant colicins were prepared and their toxic effect was tested on the sensitive bacteria transformed with plasmid harboring either cui (colicin U immunity) gene or cyi (colicin Y immunity) gene. Colicin U variants with point mutations in the hydrophobic hairpin, F576Y and G580V, were significantly less recognized by Cui, in addition to colicin U with K609R mutation localized downstream of hydrophobic hairpin.