ton b iron uptake
TRANSCRIPT
TonB and uptake of the siderophore enterobactin
Iron
Found in iron sulphur clusters and heme groups Catalyses redox reactions Comes in 2 forms
Fe(II) – soluble; can diffuse freely through outer membrane; uptake by ABC transporter; easily oxidised to Fe(III)
Fe(III) – forms insoluble hydroxides via Fenton reaction; leads to accumulation of toxic hydroxyl radicals
Iron
Important in pathogenicity
Excess iron increases virulence of many human pathogens including Escherichia, Klebsiella, Salmonella
Direct correlation between LD50 of Vibrio vulnificans and iron availability
Iron
Iron therefore kept bound to proteins in cellular environments
In mammals, bound to transferrin, lactoferrin, and ferritin among others
Free concentration in humans 10^-24M How do bacteria obtain iron?
Siderophores
Siderophores are small iron chelating molecules produced by bacteria
Have specific uptake systems
Include enterobactin
Enterobactin uptake
TonB
TonB provides energy for FepA
Energy generated by protomotive force on cytoplasmic membrane by ExbB:ExbD
TonB stores energy as conformational change
Energises FepATonB C terminal in
complex with FhuA
TonB
26kDa membrane protein, 239 AA in E. Coli 3 domains: N terminal, linker and C terminal N terminal (residues 1-32)
Interacts with ExbB and ExbD Transmembrane helix and short
cytoplasmic tail Contains Sec signal sequence for export
into the CM Replacement of this region results in loss
of interaction with ExbB and loss of activity
TonB
Linker region (residues 66-102) Proline rich; contains repeats of Glu-Pro and
Lys-Pro Highly structured conformation Can extend 10nm, allows complex to span the
periplasm Full length only necessary in high salinity
TonB C terminal
TonB C terminal interacts with outer membrane receptors
Forms a complex with receptor through B strand exchange
B strand from receptor displaces TonB B strand forming mixed B sheet
TonB C terminal (yellow) in complex with FhuA showing B sheet structure
Controversy
Multiple lines of evidence have shown TonB has the ability to dimerise with itself
Unlikely to represent in vivo interaction
Project
Aim To create a website combining literature
review with bioinformatic analysis of the enterobactin uptake system
Tools Microsoft expression web BLAST search ClustalW Jalview
Website
Can show multiple forms of media Easy to navigate to particular information Large diagrams do not obscure text Interactability
Demonstration of website
Findings of bioinformatic analysis
C terminal of TonB highly conserved Aliphatic residue at Ile193 (Leu, Ile, Val) Tyrosine-proline pairing Tyr163-Pro164 Large insertions in Synechococcus spp.