scispace - formally typeset
Search or ask a question
Journal ArticleDOI

ZnT-2, a mammalian protein that confers resistance to zinc by facilitating vesicular sequestration

15 Apr 1996-The EMBO Journal (European Molecular Biology Organization)-Vol. 15, Iss: 8, pp 1784-1791
TL;DR: It is suggested that ZnT‐2 protects zinc‐sensitive BHK cells from zinc toxicity by facilitating zinc transport into an endosomal/lysosomal compartment.
Abstract: A cDNA encoding a second zinc transporter (ZnT-2) was isolated from a rat kidney cDNA expression library by complementation of a zinc-sensitive BHK cell line. The protein predicted from the open reading frame of ZnT-2 cDNA has 359 amino acids and initiates with a CTG codon. It resembles ZnT-1 (a plasma membrane protein that stimulates zinc efflux) in overall topology in that it has six membrane-spanning domains, a histidine-rich intracellular loop and a long C-terminal tail; however, the overall amino acid identity is only 26%. Unlike ZnT-1, which is in the plasma membrane and lowers cellular zinc by stimulating zinc efflux, ZnT-2 is localized on vesicles and allows the zinc-sensitive BHK cells to accumulate zinc to levels that are much higher than non-transformed cells can tolerate. Zinc was visualized within these vesicles with zinquin, a zinc-specific fluorescent probe. The intracellular compartment that accumulates zinc is acidic as revealed by staining with acridine orange or LysoTracker. Prolonged exposure of cells expressing ZnT-2 to zinc causes an accretion of intracellular vesicles. We suggest that ZnT-2 protects these cells from zinc toxicity by facilitating zinc transport into an endosomal/lysosomal compartment.
Citations
More filters
Journal ArticleDOI
TL;DR: This review describes the workings of known metal-resistance systems in microorganisms and the transport of the 17 most important (heavy metal) elements is compared.
Abstract: We are just beginning to understand the metabolism of heavy metals and to use their metabolic functions in biotechnology, although heavy metals comprise the major part of the elements in the periodic table. Because they can form complex compounds, some heavy metal ions are essential trace elements, but, essential or not, most heavy metals are toxic at higher concentrations. This review describes the workings of known metal-resistance systems in microorganisms. After an account of the basic principles of homoeostasis for all heavy-metal ions, the transport of the 17 most important (heavy metal) elements is compared.

2,342 citations


Cites background from "ZnT-2, a mammalian protein that con..."

  • ...ZnT2 and ZnT3 are closely related and transport zinc into vesicles, ZnT2 into lysosomes (Palmiter et al. 1996a) and ZnT3 into synaptic vesicles (Palmiter et al. 1996b)....

    [...]

Journal ArticleDOI
TL;DR: The brain is a singular organ of unique biological complexity that serves as the command center for cognitive and motor function and has requirements for the highest concentrations of metal ions in the body and the highest per-weight consumption of body oxygen.
Abstract: The brain is a singular organ of unique biological complexity that serves as the command center for cognitive and motor function. As such, this specialized system also possesses a unique chemical composition and reactivity at the molecular level. In this regard, two vital distinguishing features of the brain are its requirements for the highest concentrations of metal ions in the body and the highest per-weight consumption of body oxygen. In humans, the brain accounts for only 2% of total body mass but consumes 20% of the oxygen that is taken in through respiration. As a consequence of high oxygen demand and cell complexity, distinctly high metal levels pervade all regions of the brain and central nervous system. Structural roles for metal ions in the brain and the body include the stabilization of biomolecules in static (e.g., Mg2+ for nucleic acid folds, Zn2+ in zinc-finger transcription factors) or dynamic (e.g., Na+ and K+ in ion channels, Ca2+ in neuronal cell signaling) modes, and catalytic roles for brain metal ions are also numerous and often of special demand.

1,814 citations

Journal ArticleDOI
TL;DR: Parts of zinc biology of the immune system are explored and a biological basis for the altered host resistance to infections observed during zinc deficiency and supplementation is attempted.

1,488 citations


Cites background from "ZnT-2, a mammalian protein that con..."

  • ...Recently, zinc transporters and channels mediating both the inward and outward movement of zinc were isolated from mammalian cells (216, 217)....

    [...]

Journal ArticleDOI
TL;DR: The complement of efflux systems of 63 sequenced prokaryotes was compared with that of the heavy metal resistant bacterium Ralstonia metallidurans and showed that heavy metal resistance is the result of multiple layers of resistance systems with overlapping substrate specificities, but unique functions.
Abstract: What makes a heavy metal resistant bacterium heavy metal resistant? The mechanisms of action, physiological functions, and distribution of metal-exporting proteins are outlined, namely: CBA efflux pumps driven by proteins of the resistance–nodulation–cell division superfamily, P-type ATPases, cation diffusion facilitator and chromate proteins, NreB- and CnrT-like resistance factors. The complement of efflux systems of 63 sequenced prokaryotes was compared with that of the heavy metal resistant bacterium Ralstonia metallidurans. This comparison shows that heavy metal resistance is the result of multiple layers of resistance systems with overlapping substrate specificities, but unique functions. Some of these systems are widespread and serve in the basic defense of the cell against superfluous heavy metals, but some are highly specialized and occur only in a few bacteria. Possession of the latter systems makes a bacterium heavy metal resistant.

1,333 citations


Cites background from "ZnT-2, a mammalian protein that con..."

  • ...In contrast, ZnT2 transports Zn2þ into vesicles and is therefore comparable in function to ZRC1 and COT1 [204]....

    [...]

Journal ArticleDOI
01 Mar 2001-Planta
TL;DR: Recent progress in the molecular understanding of plant metal homeostasis and tolerance is reviewed and a number of uptake transporters have been cloned as well as candidates for the vacuolar sequestration of metals are identified.
Abstract: Transition metals such as copper are essential for many physiological processes yet can be toxic at elevated levels. Other metals (e.g. lead) are nonessential and potentially highly toxic. Plants – like all other organisms – possess homeostatic mechanisms to maintain the correct concentrations of essential metal ions in different cellular compartments and to minimize the damage from exposure to nonessential metal ions. A regulated network of metal transport, chelation, trafficking and sequestration activities functions to provide the uptake, distribution and detoxification of metal ions. Some of the components of this network have now been identified: a number of uptake transporters have been cloned as well as candidate transporters for the vacuolar sequestration of metals. Chelators and chaperones are known, and evidence for intracellular metal trafficking is emerging. This recent progress in the molecular understanding of plant metal homeostasis and tolerance is reviewed.

1,327 citations

References
More filters
Journal ArticleDOI
TL;DR: Majors topics addressed in this review on zinc physiology are chemistry and biochemistry; interface of biochemistry and physiology of zinc; physiology and cell and molecular biology; and pathology.
Abstract: Majors topics addressed in this review on zinc physiology are ; 1) chemistry and biochemistry; 2) interface of biochemistry and physiology of zinc; 3) physiology and cell and molecular biology; 4) pathology

2,850 citations

Journal ArticleDOI
23 Feb 1995-Nature

1,851 citations

Journal ArticleDOI
TL;DR: Results suggest that the vacuolar type H(+)-ATPase plays a pivotal role in acidification and protein degradation in the lysosomes in vivo.

1,180 citations

Journal ArticleDOI
TL;DR: It is proposed that ZnT‐1 transports zinc out of cells and that its absence accounts for the increased sensitivity of mutant cells to zinc toxicity.
Abstract: A cDNA encoding a zinc transporter (ZnT-1) was isolated from a rat kidney cDNA expression library by complementation of a mutated, zinc-sensitive BHK cell line. This cDNA was used to isolate the homologous mouse ZnT-1 gene. The proteins predicted for these transporters contain six membrane-spanning domains, a large intracellular loop and a C-terminal tail. ZnT-1 is homologous to zinc and cobalt resistance genes of yeast. Immunocytochemistry with an antibody to a myc epitope added to the C-terminus of ZnT-1 revealed localization to the plasma membrane. Transformation of normal cells with a mutant ZnT-1 lacking the first membrane-spanning domain conferred zinc sensitivity on wild-type cells, suggesting that ZnT-1 functions as a multimer. Deletion of the first two membrane-spanning domains resulted in a non-functional molecule, whereas deletion of the C-terminal tail produced a toxic phenotype. Mutant cells have a slightly higher steady-state level of intracellular zinc and high basal expression of a zinc-dependent reporter gene compared with normal cells. Mutant cells have a lower turnover of 65Zn compared with normal cells or mutant cells transformed with ZnT-1. We propose that ZnT-1 transports zinc out of cells and that its absence accounts for the increased sensitivity of mutant cells to zinc toxicity.

739 citations

Journal ArticleDOI
TL;DR: The results suggest that prevention of apoptosis is a function of labile Zn, and that a reduction below a threshold concentration in this Zn pool induces apoptosis.
Abstract: Zinquin [(2-methyl-8-p-toluenesulphonamido-6-quinolyloxy)-acetic acid], a membrane-permeant fluorophore specific for Zn(II), was used with spectrofluorimetry and video image analysis to reveal and quantify labile intracellular Zn. Zinquin labelled human chronic-lymphocytic-leukaemia lymphocytes, rat splenocytes and thymocytes with a weak diffuse fluorescence that was quenched when intracellular Zn was chelated with NNN'N'-tetrakis-(2-pyridylmethyl)ethylenediamine (TPEN) and was greatly intensified by pretreatment of cells with the Zn ionophore pyrithione and exogenous Zn. There was substantial heterogeneity of labile Zn among ionophore-treated cells, and fluorescence was largely extranuclear. The average contents of labile Zn in human leukaemic lymphocytes, rat splenocytes and rat thymocytes were approx. 20, 31 and 14 pmol/10(6) cells respectively. Morphological changes and internucleosomal DNA fragmentation indicated substantial apoptosis in these cells when the level of intracellular labile Zn was decreased by treatment with TPEN. Conversely, increasing labile Zn by pretreatment with Zn plus pyrithione suppressed both spontaneous DNA fragmentation and that induced by the potent apoptosis-induced agents colchicine and dexamethasone. These results suggest that prevention of apoptosis is a function of labile Zn, and that a reduction below a threshold concentration in this Zn pool induces apoptosis.

488 citations