Proton-Dependent Gating and Proton Uptake by Wzx Support O-Antigen-Subunit Antiport Across the Bacterial Inner Membrane

ABSTRACT Wzx flippases are crucial for bacterial cell surface polysaccharide assembly as they transport undecaprenyl pyrophosphate-linked sugar repeat units from the cytoplasmic to the periplasmic leaflets of the inner membrane (IM) for final assembly. Our recently reported three-dimensional (3D) mo...

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Autores principales:	Salim T. Islam, Paul D. W. Eckford, Michelle L. Jones, Timothy Nugent, Christine E. Bear, Christian Vogel, Joseph S. Lam
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2013
Materias:	Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/6034fc1ffb2e4be7b0a1847a0d4781fc
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spelling	oai:doaj.org-article:6034fc1ffb2e4be7b0a1847a0d4781fc2021-11-15T15:42:47ZProton-Dependent Gating and Proton Uptake by Wzx Support O-Antigen-Subunit Antiport Across the Bacterial Inner Membrane10.1128/mBio.00678-132150-7511https://doaj.org/article/6034fc1ffb2e4be7b0a1847a0d4781fc2013-11-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.00678-13https://doaj.org/toc/2150-7511ABSTRACT Wzx flippases are crucial for bacterial cell surface polysaccharide assembly as they transport undecaprenyl pyrophosphate-linked sugar repeat units from the cytoplasmic to the periplasmic leaflets of the inner membrane (IM) for final assembly. Our recently reported three-dimensional (3D) model structure of Wzx from Pseudomonas aeruginosa PAO1 (WzxPa) displayed a cationic internal vestibule and functionally essential acidic amino acids within transmembrane segment bundles. Herein, we examined the intrinsic transport function of WzxPa following its purification and reconstitution in phospholipid liposomes. WzxPa was capable of mediating anion flux, consistent with its cationic interior. This flux was electrogenic and modified by extraliposomal pH. Mutation of the above-mentioned acidic residues (E61, D269, and D359) reduced proton (H+)-modified anion flux, showing the role of these amino acid side chains in H+-dependent transport. Wzx also mediated acidification of the proteoliposome interior in the presence of an outward anion gradient. These results indicate H+-dependent gating and H+ uptake by WzxPa and allow for the first H+-dependent antiport mechanism to be proposed for lipid-linked oligosaccharide translocation across the bacterial IM. IMPORTANCE Many bacterial cell surface polysaccharides that are important for survival and virulence are synthesized at the periplasmic leaflet of the inner membrane (IM) using precursors produced in the cytoplasm. Wzx flippases are responsible for translocation of lipid-linked sugar repeat units across the IM and had been previously suggested to simply facilitate passive substrate diffusion. Through our characterization of purified Wzx in a reconstitution system described herein, we have observed protein-dependent intrinsic transport producing a change in the electrical potential of the system, with H+ identified as the coupling ion. These results provide the first evidence for coupled (i.e., secondary active) transport by these proteins and, in conjunction with structural data, allow for an antiport mechanism to be proposed for the directed transport of lipid-linked sugar substrates across the IM. These findings bring our understanding of lipid-linked polysaccharide transporter proteins more in line with the efflux pumps to which they are evolutionarily related.Salim T. IslamPaul D. W. EckfordMichelle L. JonesTimothy NugentChristine E. BearChristian VogelJoseph S. LamAmerican Society for MicrobiologyarticleMicrobiologyQR1-502ENmBio, Vol 4, Iss 5 (2013)
institution	DOAJ
collection	DOAJ
language	EN
topic	Microbiology QR1-502
spellingShingle	Microbiology QR1-502 Salim T. Islam Paul D. W. Eckford Michelle L. Jones Timothy Nugent Christine E. Bear Christian Vogel Joseph S. Lam Proton-Dependent Gating and Proton Uptake by Wzx Support O-Antigen-Subunit Antiport Across the Bacterial Inner Membrane
description	ABSTRACT Wzx flippases are crucial for bacterial cell surface polysaccharide assembly as they transport undecaprenyl pyrophosphate-linked sugar repeat units from the cytoplasmic to the periplasmic leaflets of the inner membrane (IM) for final assembly. Our recently reported three-dimensional (3D) model structure of Wzx from Pseudomonas aeruginosa PAO1 (WzxPa) displayed a cationic internal vestibule and functionally essential acidic amino acids within transmembrane segment bundles. Herein, we examined the intrinsic transport function of WzxPa following its purification and reconstitution in phospholipid liposomes. WzxPa was capable of mediating anion flux, consistent with its cationic interior. This flux was electrogenic and modified by extraliposomal pH. Mutation of the above-mentioned acidic residues (E61, D269, and D359) reduced proton (H+)-modified anion flux, showing the role of these amino acid side chains in H+-dependent transport. Wzx also mediated acidification of the proteoliposome interior in the presence of an outward anion gradient. These results indicate H+-dependent gating and H+ uptake by WzxPa and allow for the first H+-dependent antiport mechanism to be proposed for lipid-linked oligosaccharide translocation across the bacterial IM. IMPORTANCE Many bacterial cell surface polysaccharides that are important for survival and virulence are synthesized at the periplasmic leaflet of the inner membrane (IM) using precursors produced in the cytoplasm. Wzx flippases are responsible for translocation of lipid-linked sugar repeat units across the IM and had been previously suggested to simply facilitate passive substrate diffusion. Through our characterization of purified Wzx in a reconstitution system described herein, we have observed protein-dependent intrinsic transport producing a change in the electrical potential of the system, with H+ identified as the coupling ion. These results provide the first evidence for coupled (i.e., secondary active) transport by these proteins and, in conjunction with structural data, allow for an antiport mechanism to be proposed for the directed transport of lipid-linked sugar substrates across the IM. These findings bring our understanding of lipid-linked polysaccharide transporter proteins more in line with the efflux pumps to which they are evolutionarily related.
format	article
author	Salim T. Islam Paul D. W. Eckford Michelle L. Jones Timothy Nugent Christine E. Bear Christian Vogel Joseph S. Lam
author_facet	Salim T. Islam Paul D. W. Eckford Michelle L. Jones Timothy Nugent Christine E. Bear Christian Vogel Joseph S. Lam
author_sort	Salim T. Islam
title	Proton-Dependent Gating and Proton Uptake by Wzx Support O-Antigen-Subunit Antiport Across the Bacterial Inner Membrane
title_short	Proton-Dependent Gating and Proton Uptake by Wzx Support O-Antigen-Subunit Antiport Across the Bacterial Inner Membrane
title_full	Proton-Dependent Gating and Proton Uptake by Wzx Support O-Antigen-Subunit Antiport Across the Bacterial Inner Membrane
title_fullStr	Proton-Dependent Gating and Proton Uptake by Wzx Support O-Antigen-Subunit Antiport Across the Bacterial Inner Membrane
title_full_unstemmed	Proton-Dependent Gating and Proton Uptake by Wzx Support O-Antigen-Subunit Antiport Across the Bacterial Inner Membrane
title_sort	proton-dependent gating and proton uptake by wzx support o-antigen-subunit antiport across the bacterial inner membrane
publisher	American Society for Microbiology
publishDate	2013
url	https://doaj.org/article/6034fc1ffb2e4be7b0a1847a0d4781fc
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Proton-Dependent Gating and Proton Uptake by Wzx Support O-Antigen-Subunit Antiport Across the Bacterial Inner Membrane

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