Dataset Information

Human Concentrative Nucleoside Transporter 3 (hCNT3, SLC28A3) Forms a Cyclic Homotrimer.

ABSTRACT: Many anticancer and antiviral drugs are purine or pyrimidine analogues, which use membrane transporters to cross cellular membranes. Concentrative nucleoside transporters (CNTs) mediate the salvage of nucleosides and the transport of therapeutic nucleoside analogues across plasma membranes by coupling the transport of ligands to the sodium gradient. Of the three members of the human CNT family, CNT3 has the broadest selectivity and the widest expression profile. However, the molecular mechanisms of the transporter, including how it interacts with and translocates structurally diverse nucleosides and nucleoside analogues, are unclear. Recently, the crystal structure of vcCNT showed that the prokaryotic homologue of CNT3 forms a homotrimer. In this study, we successfully expressed and purified the wild type human homologue, hCNT3, demonstrating the homotrimer by size exclusion profiles and glutaraldehyde cross-linking. Further, by creating a series of cysteine mutants at highly conserved positions guided by comparative structure models, we cross-linked hCNT3 protomers in a cell-based assay, thus showing the existence of hCNT3 homotrimers in human cells. The presence and absence of cross-links at specific locations along TM9 informs us of important structural differences between vcCNT and hCNT3. Comparative modeling of the trimerization domain and sequence coevolution analysis both indicate that oligomerization is critical to the stability and function of hCNT3. In particular, trimerization appears to shorten the translocation path for nucleosides across the plasma membrane and may allow modulation of the transport function via allostery.

SUBMITTER: Stecula A

PROVIDER: S-EPMC6917504 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature

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Human Concentrative Nucleoside Transporter 3 (hCNT3, SLC28A3) Forms a Cyclic Homotrimer.

Stecula Adrian A Schlessinger Avner A Giacomini Kathleen M KM Sali Andrej A

Biochemistry 20170629 27

Many anticancer and antiviral drugs are purine or pyrimidine analogues, which use membrane transporters to cross cellular membranes. Concentrative nucleoside transporters (CNTs) mediate the salvage of nucleosides and the transport of therapeutic nucleoside analogues across plasma membranes by coupling the transport of ligands to the sodium gradient. Of the three members of the human CNT family, CNT3 has the broadest selectivity and the widest expression profile. However, the molecular mechanisms ...[more]

PMID: 28661652

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Project description:Transporters are specialized integral membrane proteins, which mediate the passage of virtually all molecules through cell membranes. They are expressed in a broad range of human and animal tissues and play important roles in both normal and disease states. For these reasons, they are evaluated when developing and testing drugs. Two major families of drug transporters, the adenosine 5'-triphosphate-binding cassette and solute carrier transporters (SLC), have critical roles in the absorption, distribution, metabolism, and elimination of drugs. The SLC family contains known nucleoside transporters and therefore are important when nucleoside analogs are used as drugs to prevent or treat viral infections. In this study, we wanted to determine if it was possible to locate one member of the SLC family, the human concentrative nucleoside transporter 3 (CNT3) in human vaginal epithelial cells. The CNT3 protein has important roles in drug delivery, subsequent drug tissue distribution, and, hence, efficacy. Vaginal epithelial cells, taken from two human volunteers (one Caucasian and one African American), were labeled for light and electron microscopy, with a commercial antibody to a cytoplasmic domain of CNT3, the protein product of the SLC28A3 gene. Fluorescent secondary antibodies or protein A-gold were used to detect antibody binding. By electron microscopy, gold particle binding was quantified to determine labeling specificity. By light microscopy, positive labeling with anti-CNT3 antibodies was detected on human vaginal epithelial cells, but specificity to any intracellular structure was not easily determined, most likely a result of specimen preparation. Electron microscopy revealed that the CNT3 transporter protein was present predominantly on microvilli located on one side of some human vaginal epithelial cells. Quantification confirmed specific anti-CNT3 labeling over human vaginal epithelial cell microvilli. The CNT3 protein, present in the microvilli of human vaginal epithelial cells, may have a role in redistributing nucleoside homologues delivered to the vaginal tract. Transporter proteins such as CNT3 could shuttle nucleosides and their analogs through the vaginal epithelium to immune cells located in lower cell layers. Outer layers of cells, which are eventually shed from the epithelium, may remove accumulated nucleoside drug analogs from the vaginal tract.

Dataset Information

Human Concentrative Nucleoside Transporter 3 (hCNT3, SLC28A3) Forms a Cyclic Homotrimer.

Publications

Human Concentrative Nucleoside Transporter 3 (hCNT3, SLC28A3) Forms a Cyclic Homotrimer.

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