Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2011 Apr 19;108(16):6420-5.
doi: 10.1073/pnas.1100700108. Epub 2011 Apr 4.

Algae and Humans Share a Molybdate Transporter

Affiliations
Free PMC article

Algae and Humans Share a Molybdate Transporter

Manuel Tejada-Jiménez et al. Proc Natl Acad Sci U S A. .
Free PMC article

Abstract

Almost all living organisms need to obtain molybdenum from the external medium to achieve essential processes for life. Activity of important enzymes such as sulfite oxidase, aldehyde oxidase, xanthine dehydrogenase, and nitrate reductase is strictly dependent on the presence of Mo in its active site. Cells take up Mo in the form of the oxianion molybdate, but the molecular nature of the transporters is still not well known in eukaryotes. MOT1 is the first molybdate transporter identified in plant-type eukaryotic organisms, but it is absent in animal genomes. Here we report a molybdate transporter different from the MOT1 family, encoded by the Chlamydomonas reinhardtii gene MoT2, that is also present in animals including humans. The knockdown of CrMoT2 transcription leads to the deficiency of molybdate uptake activity in Chlamydomonas. In addition, heterologous expression in Saccharomyces cerevisiae of MoT2 genes from Chlamydomonas and humans support the functionality of both proteins as molybdate transporters. Characterization of CrMOT2 and HsMOT2 activities showed an apparent Km of about 550 nM that, though higher than the Km reported for MOT1, still corresponds to high affinity systems. CrMoT2 transcription is activated when extracellular molybdate concentration is low but in contrast to MoT1 is not activated by nitrate. Analysis of protein databases revealed the presence of four motifs present in all the proteins with high similarity to MOT2, that label a previously undescribed family of proteins probably related to molybdate transport. Our results open the way toward the understanding of molybdate transport as part of molybdenum homeostasis and Moco biosynthesis in animals.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Analysis of the MOT2 protein. (A) Phylogenetic tree of MOT2 homologous proteins; alignments were performed using ClustalW method, and the tree was drawn using Mega4 software. Accession numbers: Arabidopsis thaliana, AAF19685; Caenorhabditis elegans, NP_500274; Canis familiaris, XP_849836; Ciona intestinalis, XP_002129829; Chlamydomonas reinhardtii, XP_001693567; Chlorella variabilis, EFN51339; Equus caballus, XP_001504553; Homo sapiens, BAC11137; Monodelphis domestica, XP_001364537; Macaca mulatta, XP_002798648; Mus musculus, NP_598861; Micromonas pusilla, EEH53273; Nematostella vectensis, XP_001629395; Oryza sativa, NP_001065080; Ostreococcus tauri, CAL56055; Populus trichocarpa, XP_002318449; Ricinus communis, XP_002518895; Sorghum bicolor, XP_002466934; Volvox carteri, XP_002948878; Vitis vinifera, XP_002280860; Xenopus tropicalis, NP_001015939; Zea mays, ACG37381. Circles include plants, algae, worms, and animals. (B) Schematic representation of predicted CrMOT2 transmembrane topology. Dashed lines indicate the location of conserved motifs. Transmembrane topology has been predicted using TMPRED software.
Fig. 2.
Fig. 2.
Regulation of CrMoT2 transcription in response to nitrogen source and molybdenum availability. A, 8 mM ammonium; N, 4 mM nitrate; -N, nitrogen-free medium; -Mo, molybdenum-free medium. The value 1 was assigned to expression level of internal standard gene ubiquitin-ligase in each condition. Triplicate samples were used in each experiment and the experiments were repeated three times. Error bars indicate the standard deviation.
Fig. 3.
Fig. 3.
Effect of reduced CrMoT2 expression on molybdate transport in Chlamydomonas. (A) CrMoT2 transcription in antisense transformants. Quantization was made by real-time PCR. Total RNA was isolated from cells induced during 1.5 h in an 8 mM ammonium-containing medium. (B) Molybdate uptake in CrMoT2 antisense transformants. Experiments were performed in triplicate and repeated at least three times. Error bars indicate the standard deviation.
Fig. 4.
Fig. 4.
Activity of CrMOT2 expressed in Saccharomyces cerevisiae. (A) Molybdate uptake mediated by CrMOT2 compared with molybdate uptake mediated by Chlamydomonas MOT1. (B) Effect of the presence of molybdate analogue anions in molybdate transport activity mediated by CrMOT2. CrMoT2, Saccharomyces transformed with CrMoT2 cDNA; CrMoT1, Saccharomyces transformed with Chlamydomonas MoT1 cDNA; PDR196, Saccharomyces transformed with the empty expression plasmid PDR196. +S, plus 1 mM sulfate; +W, plus 20 μM tungstate. Triplicate samples were used in each experiment and the experiments were repeated three times. Error bars indicate the standard deviation.
Fig. 5.
Fig. 5.
Activity of protein HsMOT2 expressed in Saccharomyces cerevisiae. (A) Molybdate uptake mediated by HsMOT2 compared with molybdate uptake mediated by CrMOT2. (B) Effect of the presence of molybdate analogue anions in molybdate transport activity mediated by HsMOT2. HsMOT2, Saccharomyces transformed with HsMoT2 cDNA; CrMOT2, Saccharomyces transformed with CrMoT2 cDNA; PDR196, Saccharomyces transformed with the empty expression plasmid PDR196. +S, plus 1 mM sulfate; +W, plus 20 μM tungstate. Triplicate samples were used in each experiment and the experiments were repeated three times. Error bars indicate the standard deviation.

Similar articles

See all similar articles

Cited by 15 articles

See all "Cited by" articles

Publication types

MeSH terms

LinkOut - more resources

Feedback