Milon Beatrice, Wu Qin, Zou Jing, Costello Leslie C, Franklin Renty B
Department of Biomedical Sciences, Dental School, University of Maryland, Baltimore, MD 21201, USA.
Biochim Biophys Acta. 2006 Oct;1758(10):1696-701. doi: 10.1016/j.bbamem.2006.06.005. Epub 2006 Jun 7.
The proteins from the ZIP and the CDF families of zinc transporters contain a histidine-rich sequence in a loop domain located between transmembrane domains III and IV for the ZIP family and transmembrane domains IV and V for the CDF family. Topological predictions suggest that these loops are located in the cytoplasm. The loops contain a histidine-rich sequence with a variable number of histidine residues depending on the transporter. The histidine-rich sequence was postulated to serve as an extra-membrane metal binding site in these proteins. hZip1 is a human zinc transporter ubiquitously expressed. The histidine-rich motif located in the large loop of this transporter is composed of the following sequence, H(158)WHD(161). To determine if this motif is involved in the zinc transport activity of the protein, we performed site directed-mutagenesis to replace the loop histidines with alanines. Results suggest that both histidines are necessary for the zinc transport function and are not involved in the plasma membrane localization of the transporter as has been reported for the Zrt1 transporter in yeast. In addition, two histidine residues in transmembrane domains IV and V are also important in the zinc transport function. The results support an intermolecular exchange mechanism of zinc transport.
锌转运蛋白ZIP家族和CDF家族的蛋白质在跨膜结构域III和IV之间（ZIP家族）以及跨膜结构域IV和V之间（CDF家族）的环结构域中含有富含组氨酸的序列。拓扑预测表明这些环位于细胞质中。这些环含有富含组氨酸的序列，其组氨酸残基数量因转运蛋白而异。推测富含组氨酸的序列在这些蛋白质中作为膜外金属结合位点。hZip1是一种广泛表达的人类锌转运蛋白。该转运蛋白大环中富含组氨酸的基序由以下序列组成，H(158)WHD(161)。为了确定该基序是否参与蛋白质的锌转运活性，我们进行了定点诱变，用丙氨酸取代环中的组氨酸。结果表明，这两个组氨酸对于锌转运功能都是必需的，并且不像酵母中的Zrt1转运蛋白那样参与转运蛋白的质膜定位。此外，跨膜结构域IV和V中的两个组氨酸残基在锌转运功能中也很重要。这些结果支持锌转运的分子间交换机制。
