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

Abstract

The crystal structure of the C-terminal domain III of Pseudomonas aeruginosa TolA has been determined at 1.9 A Ê resolution. The fold is similar to that of the corresponding domain of Escherichia coli TolA, despite the limited amino acid sequence identity of the two proteins (20%). A pattern was discerned that conserves the fold of domain III within the wider TolA family and, moreover, reveals a relationship between TolA domain III and the C-terminal domain of the TonB transporter proteins. We propose that the TolA and TonB C-terminal domains have a common evolutionary origin and are related by means of domain swapping, with interesting mechanistic implications. We have also determined the overall shape of the didomain, domains II + III, of P.aeruginosa TolA by solution X-ray scattering. The molecule is monomericÐits elongated, stalk shape can accommodate the crystal structure of domain III at one end, and an elongated helical bundle within the portion corresponding to domain II. Based on these data, a model for the periplasmic domains of P.aeruginosa TolA is presented that may explain the inferred allosteric properties of members of the TolA family. The mechanisms of TolA-mediated entry of bateriophages in P.aeruginosa and E.coli are likely to be similar.

Dimerization of TonB Is Not Essential for Its Binding to the Outer Membrane Siderophore Receptor FhuA of Escherichia coli

“…6B). A similar structure is achieved by the dimeric TonB-77 through ␤-strand swapping (31,51). The domain-swapped TonB-77 can be generated by connecting the helix from one monomer with the ␤-strand number 3 of the other monomer (Fig.…”

“…The three-dimensional structure of the C-terminal domain of TolA from E. coli in complex with g3p (50) shows a very similar fold to the three-dimensional structure of the same domain of TolA from P. aeruginosa (31) despite an amino acid sequence identity of only 20%. Both TolA structures are composed of three ␤-strands and two ␣-helices in the order ␤-␤-␣-␣-␤ forming a three-stranded antiparallel ␤-sheet (Fig.…”

“…The first 10 N-terminal amino acids of this fragment are not visible in the electron density map because of their flexibility. The structure of another energy transducing protein, TolA from Pseudomonas aeruginosa, has been solved recently (31). Despite a sequence identity of only 24% (Lalign server) the crystal structure of the periplasmic domain of TolA shows a similar structure and topology, however without dimer formation.…”

The Structural Basis of the TIM10 Chaperone Assembly

“…The latter profile allows us to evaluate structural parameters such as the radius of gyration (R g ) and the maximum molecular dimension (D max ) from the particle distance distribution function p(r) of a monodisperse protein solution, which represents the distributions of intramolecular distances between scattering centers within a protein molecule. Further details of data reduction and analysis are as published recently (23).…”

“…Subsequently, a molecular envelope is constructed by finding a chain-compatible spatial arrangement that fits the experimental scattering data. This method has been used successfully for many proteins (23,29) with the advantage of analysis of native particles in nearly physiological conditions. The SAXS structures of individual dimers Tim9 and Tim10 are broadly similar with some subtle but detectable differences.…”