Circular dichroism and molecular modeling of theE. coli TolA periplasmic domains

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 α‐helix structure in aqueous solution and the intensity of the α‐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 α‐helices similar to coiled coil helices while domain III can adopt a globular structure. © 1999 John Wiley & Sons, Inc. Biospectroscopy 5: 189–198, 1999

Structure of the periplasmic domain of Pseudomonasaeruginosa TolA: evidence for an evolutionary relationship with the TonB transporter protein

“…Such packing would generate a distinctive geometry in which two helices of the coiled coil are parallel, yet the third is anti‐parallel to both. An earlier study has modelled E.coli TolAII as a three‐member coiled coil (Dérouiche et al ., 1999). The solution shape of P.aeruginosa TolAII + III is consistent with an elongated shape that can accommodate a bundle of three helices.…”