From conservation to structure, studies of magnetosome associated cation diffusion facilitators (CDF) proteins in Proteobacteria

ABSTRACT CzcD from Ralstonia metallidurans and ZitB from Escherichia coli are prototypes of bacterial members of the cation diffusion facilitator (CDF) protein family. Expression of the czcD gene in an E. coli mutant strain devoid of zitB and the gene for the zinc-transporting P-type ATPase zntA rendered this strain more zinc resistant and caused decreased accumulation of zinc. CzcD, purified as an amino-terminal streptavidin-tagged protein, bound Zn2+, Co2+, Cu2+, and Ni2+ but not Mg2+, Mn2+, or Cd2+, as shown by metal affinity chromatography. Histidine residues were involved in the binding of 2 to 3 mol of Zn2+ per mol of CzcD. ZitB transported 65Zn2+ in the presence of NADH into everted membrane vesicles with an apparent Km of 1.4 μM and a V max of 0.57 nmol of Zn2+ min−1 mg of protein−1. Conserved amino acyl residues that might be involved in binding and transport of zinc were mutated in CzcD and/or ZitB, and the influence on Zn2+ resistance was studied. Charged or polar amino acyl residues that were located within or adjacent to membrane-spanning regions of the proteins were essential for the full function of the proteins. Probably, these amino acyl residues constituted a pathway required for export of the heavy metal cations or for import of counter-flowing protons.

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A structural overview of the zinc transporters in the cation diffusion facilitator family

Acta Crystallographica Section D Structural Biology ◽

10.1107/s2059798319003814 ◽

2019 ◽

Vol 75 (4) ◽

pp. 357-367 ◽

Cited By ~ 8

Author(s):

Camila A. Cotrim ◽

Russell J. Jarrott ◽

Jennifer L. Martin ◽

David Drew

Keyword(s):

Metal Binding ◽

Family Members ◽

Zinc Homeostasis ◽

Cation Diffusion ◽

Intracellular Organelles ◽

Membrane Bound ◽

Cation Diffusion Facilitators ◽

Soluble C

The cation diffusion facilitators (CDFs) are a family of membrane-bound proteins that maintain cellular homeostasis of essential metal ions. In humans, the zinc-transporter CDF family members (ZnTs) play important roles in zinc homeostasis. They do this by facilitating zinc efflux from the cytoplasm to the extracellular space across the plasma membrane or into intracellular organelles. Several ZnTs have been implicated in human health owing to their association with type 2 diabetes and neurodegenerative diseases. Although the structure determination of CDF family members is not trivial, recent advances in membrane-protein structural biology have resulted in two structures of bacterial YiiPs and several structures of their soluble C-terminal domains. These data reveal new insights into the molecular mechanism of ZnT proteins, suggesting a unique rocking-bundle mechanism that provides alternating access to the metal-binding site.

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Non-Stoichiometry and Cation Tracer Diffusion Studies in the Magnetite-UlvÖSpinel Solution, (Fe,Ti)3-δO4

MRS Proceedings ◽

10.1557/proc-369-307 ◽

1994 ◽

Vol 369 ◽

Author(s):

Sanjeev Aggarwal ◽

Rudiger Dieckmann

Keyword(s):

Diffusion Coefficients ◽

Tracer Diffusion ◽

Oxygen Activity ◽

Spinel Solid Solution ◽

Low Oxygen ◽

Cation Diffusion ◽

Deviation From Stoichiometry ◽

Diffusion Studies ◽

Tracer Diffusion Coefficients ◽

Point Defect Structure

AbstractCation diffusion in the spinel solid solution (Fe1-xTix)3-δO4 (0≤ x ≤ 0.3) was investigated at 1200 ºC as a function of oxygen activity, aO2 and cationic composition, x. At different cationic compositions, cation tracer diffusion coefficients, D*Me of Me = Fe and Ti were measured as a function of oxygen activity. Plots of log DMe vs. loga0 show V-shaped curves, indicating that different types of point defects prevail at high anc low oxygen activities. Thermogravimetric experiments were conducted, using a high resolution microbalance, to determine the deviation from stoichiometry in (Fe1-xTix)3-δO4 at 1200 °C. δversus log aO2 curves are S-shaped. An analysis of the oxygen activity dependences of thecation diffusion coefficients and the deviation from stoichiometry with regardto the point defect structure suggests that at high oxygen activities cation vacancies are the predominant defects governing the deviation from stoichiometry and the diffusion ofcations. At low oxygen activities, and at small values of x, cation interstitials determine the deviation from stoichiometry, while they dominate for 0 ≤ x ≤ 0.3 inthe cation diffusion.

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