title: Shape and oligomerization state of the cytoplasmic domain of the phototaxis transducer II from Natronobacterium pharaonis.
abstract: Phototaxis allows archaea to adjust flagellar motion in response to light. In the photophobic response of Natronobacterium pharaonis, light-activated sensory rhodopsin II causes conformational changes in the transducer II protein (pHtrII), initiating the two-component signaling system analogous to bacterial chemotaxis. pHtrII's cytoplasmic domain (pHtrII-cyt) is homologous to the cytoplasmic domains of eubacterial chemotaxis receptors. Chemotaxis receptors require dimerization for activity and are in vivo-organized in large clusters. In this study we investigated the oligomerization and aggregation states of pHtrII-cyt by using chemical cross-linking, analytical gel-filtration chromatography, and small-angle neutron scattering. We show that pHtrII-cyt is monomeric in dilute buffers, but forms dimers in 4 M KCl, the physiological salt concentration for halophilic archaea. At high ammonium sulfate concentration, the protein forms higher-order aggregates. The monomeric protein has a rod-like shape, 202 A in length and 14.4 A in diameter; upon dimerization the length increases to 248 A and the diameter to 18.2 A. These results suggest that under high salt concentration the shape and oligomerization state of pHtrII-cyt are comparable to those of chemotaxis receptors.
authors.affiliation: Institute for Structural Biology and Institute of Solid-State Research, Research Center Juelich, 52425 Juelich, Germany.
authors.forename: Ivan L
authors.initials: IL
authors.lastname: Budyak
authors.forename: Vitaliy
authors.initials: V
authors.lastname: Pipich
authors.forename: Olga S
authors.initials: OS
authors.lastname: Mironova
authors.forename: Ramona
authors.initials: R
authors.lastname: Schlesinger
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Zaccai
authors.forename: Judith
authors.initials: J
authors.lastname: Klein-Seetharaman
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001704:Biopolymers / Q000737:chemistry; D002338:Carotenoids / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000737:chemistry; D018360:Crystallography, X-Ray; D019281:Dimerization; D008027:Light; D019633:Natronobacterium / Q000737:chemistry* / Q000378:metabolism; D010316:Particle Size; D052817:Phototrophic Processes / Q000502:physiology; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
chemical_list: D019843:Archaeal Proteins; D001704:Biopolymers; D003432:Cross-Linking Reagents; C434450:phototaxis receptor sensory rhodopsin II, Natronobacterium pharaonis; D002338:Carotenoids