title: Linker region of a halobacterial transducer protein interacts directly with its sensor retinal protein.
abstract: pHtrII, a pharaonis halobacterial transducer protein, possesses two transmembrane helices and forms a signaling complex with pharaonis phoborhodopsin (ppR, also called pharaonis sensory rhodopsin II, NpSRII) within the halobacterial membrane. This complex transmits a light signal to the sensory system located in the cytoplasm. It has been suggested that the linker region connecting the transmembrane region and the methylation region of pHtrII is important for binding to ppR and subsequent photosignal transduction. In this study, we present evidence to suggest that the linker region itself interacts directly with ppR in addition to the interaction in the membrane region. An in vitro pull-down assay revealed that the linker region bound to ppR, and its dissociation constant (K(D)) was estimated to be approximately 10 microM using isothermal titration calorimetry (ITC). Solution NMR analyses showed that ppR interacted with the linker region of pHtrII (pHtrII(G83)(-)(Q149)) and resulted in the broadening of many peaks, indicating structural changes within this region. These results suggest that the pHtrII linker region interacts directly with ppR. There was no demonstrable interaction between the C-terminal region of ppR (ppR(Gly224)(-)(His247)) and either the linker region (pHtrII(G83)(-)(Q149)) or the transmembrane region (pHtrII(M1)(-)(E114)) of pHtrII. On the basis of the NMR, CD, and photochemical data, we discuss the structural changes and role of the linker region of pHtrII in relation to photosignal transduction.
authors.affiliation: Laboratory of Biophysical Chemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Sudo
authors.forename: Hideyasu
authors.initials: H
authors.lastname: Okuda
authors.forename: Masaki
authors.initials: M
authors.lastname: Yamabi
authors.forename: Yuta
authors.initials: Y
authors.lastname: Fukuzaki
authors.forename: Masaki
authors.initials: M
authors.lastname: Mishima
authors.forename: Naoki
authors.initials: N
authors.lastname: Kamo
authors.forename: Chojiro
authors.initials: C
authors.lastname: Kojima
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics; D001483:Base Sequence; D001665:Binding Sites; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D019641:DNA, Archaeal / Q000235:genetics; D025602:Halorhodopsins / Q000737:chemistry* / Q000235:genetics; D008958:Models, Molecular; D019633:Natronobacterium / Q000737:chemistry* / Q000235:genetics; D019906:Nuclear Magnetic Resonance, Biomolecular; D010777:Photochemistry; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics; D025603:Sensory Rhodopsins / Q000737:chemistry* / Q000235:genetics; D015398:Signal Transduction
chemical_list: D019843:Archaeal Proteins; D019641:DNA, Archaeal; D025602:Halorhodopsins; C434451:HtrII protein, Natronobacterium pharaonis; D011993:Recombinant Fusion Proteins; D025603:Sensory Rhodopsins; C061508:sensory rhodopsin II protein, archaeal