A Thermodynamic Funnel Drives Bacterial Lipopolysaccharide Transfer in the TLR4 Pathway

Roland G. Huber, Nils A. Berglund, Vasileios Kargas, Jan K. Marzinek, Daniel A. Holdbrook, Syma Khalid, Thomas J. Piggot, Artur Schmidtchen, Peter J. Bond

Research output: Contribution to journalArticlepeer-review

22 Citations (SciVal)

Abstract

The Gram-negative bacterial outer membrane contains lipopolysaccharide, which potently stimulates the mammalian innate immune response. This involves a relay of specialized complexes culminating in transfer of lipopolysaccharide from CD14 to Toll-like receptor 4 (TLR4) and its co-receptor MD-2 on the cell surface, leading to activation of downstream inflammatory responses. In this study we develop computational models to trace the TLR4 cascade in near-atomic detail. We demonstrate through rigorous thermodynamic calculations that lipopolysaccharide molecules traversing the receptor cascade fall into a thermodynamic funnel. An affinity gradient for lipopolysaccharide is revealed upon extraction from aggregates or realistic bacterial outer membrane models and transfer through CD14 to the terminal TLR4/MD-2 receptor-co-receptor complex. We subsequently assemble viable CD14/TLR4/MD-2 oligomers at the plasma membrane surface, and observe lipopolysaccharide exchange between CD14 and TLR4/MD-2. Collectively, this work helps to unravel the key structural determinants governing endotoxin recognition in the TLR4 innate immune pathway. Huber et al. develop near-atomic computational models to simulate LPS transfer through the TLR4 pathway. These reveal that LPS recognition is favored by a thermodynamic funnel of increasing affinity along a receptor cascade, terminating in productive transfer of LPS at spontaneously assembled CD14/TLR4/MD-2 membrane complexes.

Original languageEnglish
Pages (from-to)1151-1161.e4
JournalStructure
Volume26
Issue number8
DOIs
Publication statusPublished - 2018 Aug

Subject classification (UKÄ)

  • Medical Biotechnology

Keywords

  • cluster of differentiation 14 (CD14)
  • coarse-grained (CG) models
  • free-energy calculations
  • lipopolysaccharide (LPS)
  • molecular dynamics (MD) simulations
  • myeloid differentiation factor 2 (MD-2)
  • oligomerization
  • OmpF porin
  • toll-like receptor 4 (TLR4)

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