TonB-Dependent Transporters in Sphingomonads: Unraveling Their Distribution and Function in Environmental Adaptation.

Devyani Samantarrai,Dayananda Siddavattam,Ramurthy Gudla,Annapoorni Lakshman Sagar

doi:10.3390/microorganisms8030359

Devyani Samantarrai, Dayananda Siddavattam + Show 2 more

Open Access

https://doi.org/10.3390/microorganisms8030359

Copy DOI

Journal: Microorganisms	Publication Date: Mar 3, 2020
Citations: 19	License type: CC BY 4.0

Affiliation: University of Hyderabad

Abstract

TonB-dependent transport system plays a critical role in the transport of nutrients across the energy-deprived outer membrane of Gram-negative bacteria. It contains a specialized outer membrane TonB-dependent transporter (TBDT) and energy generating (ExbB/ExbD) and transducing (TonB) inner membrane multi-protein complex, called TonB complex. Very few TonB complex protein-coding sequences exist in the genomes of Gram-negative bacteria. Interestingly, the TBDT coding alleles are phenomenally high, especially in the genomes of bacteria surviving in complex and stressful environments. Sphingomonads are known to survive in highly polluted environments using rare, recalcitrant, and toxic substances as their sole source of carbon. Naturally, they also contain a huge number of TBDTs in the outer membrane. Out of them, only a few align with the well-characterized TBDTs. The functions of the remaining TBDTs are not known. Predictions made based on genome context and expression pattern suggest their involvement in the transport of xenobiotic compounds across the outer membrane.

Highlights

The outer membrane of Gram-negative bacteria performs several important functions
The active transport mechanism of the outer membrane is known as TonB-dependent transport system
The proton motif force (PMF) components ExbB/ExbD generate energy by pumping protons across the inner membrane, while TonB transduces this energy to the outer membrane-localized TonB-dependent transporter (TBDT)

Summary

Introduction

The outer membrane of Gram-negative bacteria performs several important functions. It acts as a barrier to prevent the entry of antibiotics and other toxic chemicals and protects the cell wall by denying access to cell wall degrading enzymes. Certain scarcely available nutrients depend on active transport to cross the energy-deprived outer membrane. The system contains two components, the inner membrane-associated TonB complex and an outer membrane-associated TonB-dependent transporter (TBDT). The TonB complex has unique role in outer membrane transport. The PMF components ExbB/ExbD generate energy by pumping protons across the inner membrane, while TonB transduces this energy to the outer membrane-localized TBDT. TBDT facilitate the transduction transport scarcely available nutrients across the outer membrane. TBDT possesses of energy required to transport scarcely available nutrients across the outer membrane. N-terminal globular domain, through its unique structural features, establishes cross-talk membrane-localized. TonB harvests energy generated by PMF components for the structural transition of TBDT. The gut microbiome sequences show an genomes of cells isolated from harsh environments [8].

The TonB-Dependent Transport System

Unique TonB Complex in Sphingobium fuliginis