title: Structural basis for amino-acid recognition and transmembrane signalling by tandem Per-Arnt-Sim (tandem PAS) chemoreceptor sensory domains.
abstract: Chemotaxis, mediated by methyl-accepting chemotaxis protein (MCP) receptors, plays an important role in the ecology of bacterial populations. This paper presents the first crystallographic analysis of the structure and ligand-induced conformational changes of the periplasmic tandem Per-Arnt-Sim (PAS) sensing domain (PTPSD) of a characterized MCP chemoreceptor. Analysis of the complex of the Campylobacter jejuni Tlp3 PTPSD with isoleucine (a chemoattractant) revealed that the PTPSD is a dimer in the crystal. The two ligand-binding sites are located in the membrane-distal PAS domains on the faces opposite to the dimer interface. Mutagenesis experiments show that the five strongly conserved residues that stabilize the main-chain moiety of isoleucine are essential for binding, suggesting that the mechanism by which this family of chemoreceptors recognizes amino acids is highly conserved. Although the fold and mode of ligand binding of the PTPSD are different from the aspartic acid receptor Tar, the structural analysis suggests that the PTPSDs of amino-acid chemoreceptors are also likely to signal by a piston displacement mechanism. The PTPSD fluctuates between piston (C-terminal helix) `up' and piston `down' states. Binding of an attractant to the distal PAS domain locks it in the closed form, weakening its association with the proximal domain and resulting in the transition of the latter into an open form, concomitant with a downward (towards the membrane) 4 Å piston displacement of the C-terminal helix. In vivo, this movement would generate a transmembrane signal by driving a downward displacement of the transmembrane helix 2 towards the cytoplasm.
authors.affiliation: Department of Microbiology, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Yu C
authors.initials: YC
authors.lastname: Liu
authors.affiliation: Department of Microbiology, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Mayra A
authors.initials: MA
authors.lastname: Machuca
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Simone A
authors.initials: SA
authors.lastname: Beckham
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Menachem J
authors.initials: MJ
authors.lastname: Gunzburg
authors.affiliation: Department of Microbiology, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Anna
authors.initials: A
authors.lastname: Roujeinikova
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002169:Campylobacter Infections / Q000382:microbiology; D016123:Campylobacter jejuni / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D002633:Chemotaxis; D018360:Crystallography, X-Ray; D007532:Isoleucine / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D000072236:Methyl-Accepting Chemotaxis Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D055503:Protein Multimerization; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D015398:Signal Transduction
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; D007532:Isoleucine; C116037:PAS domain kinases; D017346:Protein Serine-Threonine Kinases
keywords: chemotaxis; methyl-accepting protein; sensing domain