title: On the role of a specific insert in acetate permeases (ActP) for tellurite uptake in bacteria: Functional and structural studies.
abstract: The oxyanion tellurite (TeO32-) is extremely toxic to bacterial cells. In Rhodobacter capsulatus, tellurite enters the cytosol by means of the high uptake-rate acetate permease RcActP2, encoded by one of the three actP genes present in this species (actP1, actP2 and actP3). Conversely, in Escherichia coli a low rate influx of the oxyanion is measured, which depends mainly on the phosphate transporter EcPitA, even though E. coli contains its own EcActP acetate permease. Here we report that when the actP2 gene from R. capsulatus is expressed in wild-type E. coli HB101 and in E. coli JW3460 ΔpitA mutant, the cellular intake of tellurite increases up to four times, suggesting intrinsic structural differences between EcActP and RcActP2. Indeed, a sequence analysis indicated the presence in RcActP2 of an insert of 15-16 residues, located between trans-membrane (TM) helices 6 and 7, which is absent in both EcActP and RcActP1. Based on this observation, the molecular models of homodimeric RcActP1 and RcActP2 were calculated and analyzed. In the RcActP2 model, the insert induces a perturbation in the conformation of the loop between TM helices 6 and 7, located at the RcActP2 dimerization interface. This perturbation opens a cavity on the periplasmic side that is closed, instead, in the RcActP1 model. This cavity also features an increase of the positive electric potential on the protein surface, an effect ascribed to specific residues Lys261, Lys281 and Arg560. We propose that this positively charged patch in RcActP2 is involved in recognition and translocation of the TeO32-anion, attributing to RcActP2 a greater ability as compared to RcActP1 to transport this inorganic poison inside the cells.
authors.affiliation: Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy. Electronic address: roberto.borghese@unibo.it.
authors.forename: Roberto
authors.initials: R
authors.lastname: Borghese
authors.affiliation: Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Canducci
authors.affiliation: Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Musiani
authors.affiliation: Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy.
authors.forename: Martina
authors.initials: M
authors.lastname: Cappelletti
authors.affiliation: Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Ciurli
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, Canada.
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Turner
authors.affiliation: Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Zannoni
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001693:Biological Transport, Active; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D027501:Monocarboxylic Acid Transporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D016354:Rhodobacter capsulatus / Q000235:genetics / Q000378:metabolism; D013691:Tellurium / Q000493:pharmacokinetics / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D027501:Monocarboxylic Acid Transporters; C026660:tellurous acid; D013691:Tellurium
keywords: Acetate permeases; ActP1; ActP2; Escherichia coli; Rhodobacter capsulatus; Tellurite uptake