title: Structure-function of cyanobacterial outer-membrane protein, Slr1270: homolog of Escherichia coli drug export/colicin import protein, TolC.
abstract: Compared to thylakoid and inner membrane proteins in cyanobacteria, no structure-function information is available presently for integral outer-membrane proteins (OMPs). The Slr1270 protein from the cyanobacterium Synechocystis 6803, over-expressed in Escherichia coli, was refolded, and characterized for molecular size, secondary structure, and ion-channel function. Refolded Slr1270 displays a single band in native-electrophoresis, has an α-helical content of 50-60%, as in E. coli TolC with which it has significant secondary-structure similarity, and an ion-channel function with a single-channel conductance of 80-200pS, and a monovalent ion (K(+):Cl(-)) selectivity of 4.7:1. The pH-dependence of channel conductance implies a role for carboxylate residues in channel gating, analogous to that in TolC.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, IN, United States; Molecular Biology Division, Bhabha Atomic Research Centre, Mumbai, India.
authors.forename: Rachna
authors.initials: R
authors.lastname: Agarwal
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, IN, United States; Institute of Basic Problems of Biology, Russian Academy of Sciences, Puschino, Moscow Region, Russian Federation.
authors.forename: Stanislav
authors.initials: S
authors.lastname: Zakharov
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, IN, United States.
authors.forename: S Saif
authors.initials: SS
authors.lastname: Hasan
authors.affiliation: Pasarow Mass Spectrometry Laboratory, NPI-Semel Institute for Neuroscience and Human Behavior, UCLA, Los Angeles, CA, United States.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Ryan
authors.affiliation: Pasarow Mass Spectrometry Laboratory, NPI-Semel Institute for Neuroscience and Human Behavior, UCLA, Los Angeles, CA, United States.
authors.forename: Julian P
authors.initials: JP
authors.lastname: Whitelegge
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, IN, United States. Electronic address: waclab@purdue.edu.
authors.forename: William A
authors.initials: WA
authors.lastname: Cramer
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D008051:Lipid Bilayers / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D055503:Protein Multimerization; D058849:Protein Refolding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D046939:Synechocystis / Q000737:chemistry*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D008051:Lipid Bilayers; D026901:Membrane Transport Proteins; C073126:tolC protein, E coli
keywords: Cyanobacteria; Ion channel; Outer-membrane proteins; Secondary-structure; Slr1270; TolC