Structure-Activity Relationship Study Reveals the Molecular Basis for Specific Sensing of Hydrophobic Amino Acids by the Campylobacter jejuni Chemoreceptor Tlp3

Mohammad F. Khan, Mayra A. Machuca, Mohammad M. Rahman, Cengiz Koç, Raymond S. Norton, Brian J. Smith, Anna Roujeinikova

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Chemotaxis is an important virulence factor of the foodborne pathogen Campylobacter jejuni. Inactivation of chemoreceptor Tlp3 reduces the ability of C. jejuni to invade human and chicken cells and to colonise the jejunal mucosa of mice. Knowledge of the structure of the ligand-binding domain (LBD) of Tlp3 in complex with its ligands is essential for a full understanding of the molecular recognition underpinning chemotaxis. To date, the only structure in complex with a signal molecule is Tlp3 LBD bound to isoleucine. Here, we used in vitro and in silico screening to identify eight additional small molecules that signal through Tlp3 as attractants by directly binding to its LBD, and determined the crystal structures of their complexes. All new ligands (leucine, valine, α-amino-N-valeric acid, 4-methylisoleucine, β-methylnorleucine, 3-methylisoleucine, alanine, and phenylalanine) are nonpolar amino acids chemically and structurally similar to isoleucine. X-ray crystallographic analysis revealed the hydrophobic side-chain binding pocket and conserved protein residues that interact with the ammonium and carboxylate groups of the ligands determine the specificity of this chemoreceptor. The uptake of hydrophobic amino acids plays an important role in intestinal colonisation by C. jejuni, and our study suggests that C. jejuni seeks out hydrophobic amino acids using chemotaxis.

Original languageEnglish
Article number744
Number of pages26
JournalBiomolecules
Volume10
Issue number5
DOIs
Publication statusPublished - 11 May 2020

Keywords

  • Campylobacter jejuni
  • chemoreceptor
  • dCache
  • high-throughput screening
  • methyl-accepting chemotaxis protein

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