title: The Role of Flexible Loops in Folding, Trafficking and Activity of Equilibrative Nucleoside Transporters.
abstract: Equilibrative nucleoside transporters (ENTs) are integral membrane proteins, which reside in plasma membranes of all eukaryotic cells and mediate thermodynamically downhill transport of nucleosides. This process is essential for nucleoside recycling, and also plays a key role in terminating adenosine-mediated cellular signaling. Furthermore, ENTs mediate the uptake of many drugs, including anticancer and antiviral nucleoside analogues. The structure and mechanism, by which ENTs catalyze trans-membrane transport of their substrates, remain unknown. To identify the core of the transporter needed for stability, activity, and for its correct trafficking to the plasma membrane, we have expressed human ENT deletion mutants in Xenopus laevis oocytes and determined their localization, transport properties and susceptibility to inhibition. We found that the carboxyl terminal trans-membrane segments are essential for correct protein folding and trafficking. In contrast, the soluble extracellular and intracellular loops appear to be dispensable, and must be involved in the fine-tuning of transport regulation.
authors.affiliation: Department of Physiology and Biophysics, Weill Cornell Medical College in Qatar, Qatar foundation, Education City, Doha, Qatar.
authors.forename: Jaya
authors.initials: J
authors.lastname: Aseervatham
authors.affiliation: Department of Physiology and Biophysics, Weill Cornell Medical College, New York, United States of America.
authors.forename: Lucky
authors.initials: L
authors.lastname: Tran
authors.affiliation: Department of Physiology and Biophysics, Weill Cornell Medical College in Qatar, Qatar foundation, Education City, Doha, Qatar.
authors.forename: Khaled
authors.initials: K
authors.lastname: Machaca
authors.affiliation: Department of Physiology and Biophysics, Weill Cornell Medical College, New York, United States of America.
authors.forename: Olga
authors.initials: O
authors.lastname: Boudker
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D033721:Equilibrative Nucleoside Transporter 1 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D017510:Protein Folding; D017433:Protein Structure, Secondary; D021381:Protein Transport / Q000502:physiology; D017384:Sequence Deletion; D014982:Xenopus laevis
chemical_list: D033721:Equilibrative Nucleoside Transporter 1; C438649:SLC29A1 protein, human