Structure-function analysis of HKE4, a member of the new LIV-1 subfamily of zinc transporters.
The KE4 proteins are an emerging group of proteins with little known functional data. In the present study, we report the first characterization of the recombinant human KE4 protein in mammalian cells. The KE4 sequences are included in the subfamily of ZIP (Zrt-, Irt-like Proteins) zinc transporters, which we have termed LZT (LIV-1 subfamily of ZIP zinc Transporters). All these LZT sequences contain similarities to ZIP transporters, including the consensus sequence in transmembrane domain IV, which is essential for zinc transport. However, the new LZT subfamily can be separated from other ZIP transporters by the presence of a highly conserved potential metalloprotease motif (HEXPHEXGD) in transmembrane domain V. Here we report the location of HKE4 on intracellular membranes, including the endoplasmic reticulum, and its ability to increase the intracellular free zinc as measured with the zinc-specific fluorescent dye, Newport Green, in a time-, temperature- and concentration-dependent manner. This is in contrast with the zinc influx ability of another LZT protein, LIV-1, which was due to its plasma membrane location. Therefore we have added to the functionality of LZT proteins by reporting their ability to increase intracellular-free zinc, whether they are located on the plasma membrane or on intracellular membranes. This result, in combination with the crucial role that zinc plays in cell growth, emphasizes the importance of this new LZT subfamily, including the KE4 sequences, in the control of intracellular zinc homoeostasis, aberrations of which can lead to diseases such as cancer, immunological disorders and neurological dysfunction.
Taylor
Kathryn M
KM
Tenovus Cancer Research Centre, Welsh School of Pharmacy, Cardiff University, Redwood Building, King Edward VII Avenue, Cardiff CF10 3XF, UK. Taylorkm@cardiff.ac.uk
Morgan
Helen E
HE
Johnson
Andrea
A
Nicholson
Robert I
RI
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D016466:CHO Cells; D002352:Carrier Proteins / Q000737:chemistry* / Q000145:classification / Q000378:metabolism*; D027682:Cation Transport Proteins; D006224:Cricetinae; D006801:Humans; D007425:Intracellular Membranes / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship; D014018:Tissue Distribution; D015032:Zinc / Q000378:metabolism
D002352:Carrier Proteins; D027682:Cation Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D011994:Recombinant Proteins; C102227:SLC39A7 protein, human; C017800:zinc-binding protein; D015032:Zinc