Novel channel enzyme fusion proteins confer arsenate resistance.
Steady exposure to environmental arsenic has led to the evolution of vital cellular detoxification mechanisms. Under aerobic conditions, a two-step process appears most common among microorganisms involving reduction of predominant, oxidized arsenate (H(2)As(V)O(4)(-)/HAs(V)O(4)(2-)) to arsenite (As(III)(OH)(3)) by a cytosolic enzyme (ArsC; Escherichia coli type arsenate reductase) and subsequent extrusion via ArsB (E. coli type arsenite transporter)/ACR3 (yeast type arsenite transporter). Here, we describe novel fusion proteins consisting of an aquaglyceroporin-derived arsenite channel with a C-terminal arsenate reductase domain of phosphotyrosine-phosphatase origin, providing transposable, single gene-encoded arsenate resistance. The fusion occurred in actinobacteria from soil, Frankia alni, and marine environments, Salinispora tropica; Mycobacterium tuberculosis encodes an analogous ACR3-ArsC fusion. Mutations rendered the aquaglyceroporin channel more polar resulting in lower glycerol permeability and enhanced arsenite selectivity. The arsenate reductase domain couples to thioredoxin and can complement arsenate-sensitive yeast strains. A second isoform with a nonfunctional channel may use the mycothiol/mycoredoxin cofactor pool. These channel enzymes constitute prototypes of a novel concept in metabolism in which a substrate is generated and compartmentalized by the same molecule. Immediate diffusion maintains the dynamic equilibrium and prevents toxic accumulation of metabolites in an energy-saving fashion.
Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-Universität zu Kiel, 24118 Kiel, Germany.
Binghua
B
Wu
Jie
J
Song
Eric
E
Beitz
D051397:Aquaglyceroporins / Q000096:biosynthesis / Q000235:genetics; D001149:Arsenates / Q000494:pharmacology*; D001419:Bacteria / Q000235:genetics / Q000378:metabolism*; D024881:Drug Resistance, Bacterial / Q000187:drug effects* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000096:biosynthesis* / Q000235:genetics; D016623:Ion Pumps / Q000096:biosynthesis* / Q000235:genetics; D026901:Membrane Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D009097:Multienzyme Complexes / Q000096:biosynthesis* / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis* / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000096:biosynthesis* / Q000235:genetics; D013723:Teratogens / Q000494:pharmacology*
C109281:ACR3 protein, S cerevisiae; D051397:Aquaglyceroporins; D001149:Arsenates; D029968:Escherichia coli Proteins; D016623:Ion Pumps; D026901:Membrane Transport Proteins; D009097:Multienzyme Complexes; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D013723:Teratogens; C486481:ArsAB ATPase, E Coli; C025657:arsenic acid