NMR structure of the C-terminal domain of TonB protein from Pseudomonas aeruginosa

PeerJ. 2018 Aug 27;6:e5412. doi: 10.7717/peerj.5412. eCollection 2018.

Abstract

The TonB protein plays an essential role in the energy transduction system to drive active transport across the outer membrane (OM) using the proton-motive force of the cytoplasmic membrane of Gram-negative bacteria. The C-terminal domain (CTD) of TonB protein is known to interact with the conserved TonB box motif of TonB-dependent OM transporters, which likely induces structural changes in the OM transporters. Several distinct conformations of differently dissected CTDs of Escherichia coli TonB have been previously reported. Here we determined the solution NMR structure of a 96-residue fragment of Pseudomonas aeruginosa TonB (PaTonB-96). The structure shows a monomeric structure with the flexible C-terminal region (residues 338-342), different from the NMR structure of E. coli TonB (EcTonB-137). The extended and flexible C-terminal residues are confirmed by 15N relaxation analysis and molecular dynamics simulation. We created models for the PaTonB-96/TonB box interaction and propose that the internal fluctuations of PaTonB-96 makes it more accessible for the interactions with the TonB box and possibly plays a role in disrupting the plug domain of the TonB-dependent OM transporters.

Keywords: 15N relaxation; BtuB; Molecular dynamics; NMR; NMR structure; Outer membrane transporter; Protein structure; Pseudomonas aeruginosa; TonB; TonB-dependent energy transduction.

Grant support

This work was supported by Sigrid Jusélius Foundation, the Academy of Finland (131413, 137995 and 277335) and CSC-IT Center for Science Ltd. Finland (the allocation of computational resources). The Finnish Biological NMR center is supported by Biocenter Finland and HiLIFE-INFRA. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.