Functional characterization and metal ion specificity of the metal-citrate complex transporter from Streptomyces coelicolor

Joshua J. Lensbouer, Ami Patel, Joseph P. Sirianni, Robert P. Doyle

Research output: Contribution to journalArticle

18 Scopus citations

Abstract

Secondary transporters of citrate in complex with metal ions belong to the bacterial CitMHS family, about which little is known. The transport of metal-citrate complexes in Streptomyces coelicolor has been investigated. The best cofactor for citrate uptake in Streptomyces coelicolor is Fe3+, but uptake was also noted for Ca2+, Pb2+, Ba2+, and Mn2+. Uptake was not observed with the Mg2+, Ni 2+, or Co2+ cofactor. The transportation of iron-and calcium-citrate makes these systems unique among the CitMHS family members reported to date. No complementary uptake akin to that observed for the CitH (Ca2+, Ba2+, Sr2+) and CitM (Mg2+, Ni2+, Mn2+, Co2+, Zn2+) systems of Bacillus subtilis was noted. Competitive experiments using EGTA confirmed that metal-citrate complex formation promoted citrate uptake. Uptake of free citrate was not observed. The open reading frame postulated as being responsible for the metal-citrate transport observed in Streptomyces coelicolor was cloned and overexpressed in Escherichia coli strains with the primary Fe 3+-citrate transport system (fecABCDE) removed. Functional expression was successful, with uptake of Ca2+-citrate, Fe3+- citrate, and Pb2+-citrate observed. No free-citrate transport was observed in IPTG (isopropyl-β-D-thiogalactopyranoside)-induced or -uninduced E. coli. Metabolism of the Fe3+-citrate and Ca 2+-citrate complexes, but not the Pb2+-citrate complex, was observed. Rationalization is based on the difference in metal-complex coordination upon binding of the metal by citrate.

Original languageEnglish (US)
Pages (from-to)5616-5623
Number of pages8
JournalJournal of bacteriology
Volume190
Issue number16
DOIs
StatePublished - Aug 1 2008

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

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