title: The light-activated proton pump Bop I of the archaeon Haloquadratum walsbyi.
abstract: We have isolated and characterized the light-driven proton pump Bop I from the ultrathin square archaeon Haloquadratum walsbyi, the most abundant component of the dense microbial community inhabiting hypersaline environments. The disruption of cells by hypo-osmotic shock yielded Bop I retinal protein highly enriched membranes, which contain one main 27 kDa protein band together with a high content of the carotenoid bacterioruberin. Light-induced pH changes were observed in suspensions of Bop I retinal protein-enriched membranes under sustained illumination. Solubilization of H. walsbyi cells with Triton X-100, followed by phenyl-Sepharose chromatography, resulted in isolation of two purified Bop I retinal protein bands; mass spectrometry analysis revealed that the Bop I was present as only protein in both the bands. The study of light/dark adaptations, M-decay kinetics, responses to titration with alkali in the dark and endogenous lipid compositions of the two Bop I retinal protein bands showed functional differences that could be attributed to different protein aggregation states. Proton-pumping activity of Bop I during the photocycle was observed in liposomes constituted of archaeal lipids. Similarities and differences of Bop I with other archaeal proton-pumping retinal proteins will be discussed.
authors.affiliation: Department of Basic Medical Sciences, University of Bari Aldo Moro, Bari, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Lobasso
authors.forename: Patrizia
authors.initials: P
authors.lastname: Lopalco
authors.forename: Rita
authors.initials: R
authors.lastname: Vitale
authors.forename: Matilde Sublimi
authors.initials: MS
authors.lastname: Saponetti
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Capitanio
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Mangini
authors.forename: Francesco
authors.initials: F
authors.lastname: Milano
authors.forename: Massimo
authors.initials: M
authors.lastname: Trotta
authors.forename: Angela
authors.initials: A
authors.lastname: Corcelli
mesh_terms: D001483:Base Sequence; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D006216:Halobacteriaceae / Q000378:metabolism / Q000528:radiation effects*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D017494:Proton Pumps / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet
chemical_list: D017931:DNA Primers; D017494:Proton Pumps