title: The crystal structure of the tandem-PAS sensing domain of Campylobacter jejuni chemoreceptor Tlp1 suggests indirect mechanism of ligand recognition.
abstract: Chemotaxis and motility play an important role in the colonisation of avian and human hosts by Campylobacter jejuni. Chemotactic recognition of extracellular signals is mediated by the periplasmic sensing domain of methyl-accepting chemotactic proteins (membrane-embedded receptors). In this work, we report a high-resolution structure of the periplasmic sensing domain of transducer-like protein 1 (Tlp1), an aspartate receptor of C. jejuni. Crystallographic analysis revealed that it contains two Per-Arnt-Sim (PAS) subdomains. An acetate and chloride ions (both from the crystallisation buffer) were observed bound to the membrane-proximal and membrane-distal PAS subdomains, respectively. Surprisingly, despite being crystallised in the presence of aspartate, the structure did not show any electron density corresponding to this amino acid. Furthermore, no binding between the sensing domain of Tlp1 and aspartate was detected by microcalorimetric experiments. These structural and biophysical data suggest that Tlp1 does not sense aspartate directly; instead, ligand recognition is likely to occur indirectly via an as yet unidentified periplasmic binding protein.
authors.affiliation: Infection and Immunity Program, Monash Biomedicine Discovery Institute, Australia; Department of Microbiology, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Mayra A
authors.initials: MA
authors.lastname: Machuca
authors.affiliation: Infection and Immunity Program, Monash Biomedicine Discovery Institute, Australia; Department of Microbiology, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Yu C
authors.initials: YC
authors.lastname: Liu
authors.affiliation: Infection and Immunity Program, Monash Biomedicine Discovery Institute, Australia; Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Simone A
authors.initials: SA
authors.lastname: Beckham
authors.affiliation: Infection and Immunity Program, Monash Biomedicine Discovery Institute, Australia; Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Menachem J
authors.initials: MJ
authors.lastname: Gunzburg
authors.affiliation: Infection and Immunity Program, Monash Biomedicine Discovery Institute, Australia; Department of Microbiology, Monash University, Clayton, Victoria 3800, Australia; Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia. Electronic address: Anna.Roujeinikova@monash.edu.
authors.forename: Anna
authors.initials: A
authors.lastname: Roujeinikova
mesh_terms: D001224:Aspartic Acid / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D016123:Campylobacter jejuni / Q000737:chemistry* / Q000378:metabolism; D002633:Chemotaxis / Q000502:physiology; D018360:Crystallography, X-Ray; D008024:Ligands; D008958:Models, Molecular; D000072417:Protein Domains; D017433:Protein Structure, Secondary; D017459:Receptors, Amino Acid / Q000737:chemistry* / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D008024:Ligands; D017459:Receptors, Amino Acid; D011994:Recombinant Proteins; C031959:aspartic acid receptor; D001224:Aspartic Acid
keywords: Chemotaxis; Crystal structure; Methyl-accepting protein; Sensing domain