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  • Title: Circular dichroism and molecular modeling of the E. coli TolA periplasmic domains.
    Author: Derouiche R, Lloubès R, Sasso S, Bouteille H, Oughideni R, Lazdunski C, Loret E.
    Journal: Biospectroscopy; 1999; 5(3):189-98. PubMed ID: 10380085.
    Abstract:
    Colicins are killer proteins that use envelope proteins from the outer and the inner membranes to reach their cellular target in susceptible cells of Escherichia coli. Each group A colicin uses a combination of Tol proteins to cross the outer membrane of gram-negative bacteria and to exert their killing activity. The TolA protein, necessary for the import of all the group A colicins, is a 421-amino acid residue protein composed of three domains (TolAI, TolAII, and TolAIII). TolAIII interacts with the N-terminal domain of colicin A (AT1). Analytical ultracentrifugation reveals that TolAII and TolAIII are monomer structures, TolAII has an elongated structure, and TolAIII is rather globular. Circular dichroism (CD) spectra were done with TolAII-III, TolAII, TolAIII, AT1, and the AT1-TolAII-III complex. TolA CD spectra reveal the presence of alpha-helix structure in aqueous solution and the intensity of the a-helix signal is the highest with TolAII. Few structural changes are observed with the complex AT1-TolAII-III. Molecular modeling was done for TolAII-III, taking into account CD and ultracentrifugation data and show that domain II can adopt a barrel structure made of three twisted alpha-helices similar to coiled coil helices while domain III can adopt a globular structure.
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