title: Crithidia fasciculata adenosine transporter 1 (CfAT1), a novel high-affinity equilibrative nucleoside transporter specific for adenosine.
abstract: Most eukaryotic organisms including protozoans like Crithidia, Leishmania, and Plasmodium encode a repertoire of equilibrative nucleoside transporters (ENTs). Using genomic sequencing data from Crithidia fasciculata, we discovered that this organism contains multiple ENT genes of highly similar sequence to the previously cloned and characterized adenosine transporter CfNT1: CfAT1 and CfNT3, and an allele of CfAT1, named CfAT1.2. Characterization of CfAT1 shows that it is an adenosine-only transporter, 87% identical to CfNT1 in protein sequence, with a 50-fold lower Km for adenosine. Site directed mutation of a key residue in transmembrane domain 4 (TM4) in both CfNT1 and CfAT1 shows that lysine at this position results in a high affinity phenotype, while threonine decreases adenosine affinity in both transporters. These results show that C. fasciculata has at least two adenosine transporters, and that as in other protozoan ENTs, a lysine residue in TM4 plays a key role in ligand affinity.
authors.affiliation: Pacific University School of Pharmacy, 222 SE 8th Avenue, Suite 451, Hillsboro, OR 97123, USA. Electronic address: csarendt@gmail.com.
authors.forename: Cassandra S
authors.initials: CS
authors.lastname: Arendt
mesh_terms: D000241:Adenosine / Q000378:metabolism*; D000595:Amino Acid Sequence; D001692:Biological Transport; D003001:Cloning, Molecular; D016831:Crithidia fasciculata / Q000737:chemistry / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D056986:Euglenozoa Infections / Q000469:parasitology*; D006801:Humans; D008969:Molecular Sequence Data; D033703:Nucleoside Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D013045:Species Specificity
chemical_list: D033703:Nucleoside Transport Proteins; D015800:Protozoan Proteins; C444719:adenosine transporter; D000241:Adenosine
keywords: Adenosine; Crithidia fasciculata; Equilibrative nucleoside transporter; Ligand affinity; Purine metabolism