title: Two allelic isoforms of the serotonin transporter from Schistosoma mansoni display electrogenic transport and high selectivity for serotonin.
abstract: The human blood fluke Schistosoma mansoni is the primary cause of schistosomiasis, a debilitating disease that affects 200 million individuals in over 70 countries. The biogenic amine serotonin is essential for the survival of the parasite and serotonergic proteins are potential novel drug targets for treating schistosomiasis. Here we characterize two novel serotonin transporter gene transcripts, SmSERT-A and SmSERT-B, from S.mansoni. Southern blot analysis shows that the two mRNAs are the products of different alleles of a single SmSERT gene locus. The two SmSERT forms differ in three amino acid positions near the N-terminus of the protein. Both SmSERTs are expressed in the adult form and in the sporocyst form (infected snails) of the parasite, but are absent from all other stages of the parasite's complex life cycle. Heterologous expression of the two cDNAs in mammalian cells resulted in saturable, sodium-dependent serotonin transport activity with an apparent affinity for serotonin comparable to that of the human serotonin transporter. Although the two SmSERTs are pharmacologically indistinguishable from each other, efflux experiments reveal notably higher substrate selectivity for serotonin compared with their mammalian counterparts. Several well-established substrates for human SERT including (+/-)MDMA, S-(+)amphetamine, RU 24969, and m-CPP are not transported by SmSERTs, underscoring the higher selectivity of the schistosomal isoforms. Voltage-clamp recordings of SmSERT substrate-elicited currents confirm the substrate selectivity observed in efflux experiments and suggest that it may be possible to exploit the electrogenic nature of SmSERT to screen for compounds that target the parasite in vivo.
authors: Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA.
authors: Andréia C K
authors: AC
authors: Fontana
authors: Mark S
authors: MS
authors: Sonders
authors: Olavo S
authors: OS
authors: Pereira-Junior
authors: Matty
authors: M
authors: Knight
authors: Jonathan A
authors: JA
authors: Javitch
authors: Vanderlei
authors: V
authors: Rodrigues
authors: Susan G
authors: SG
authors: Amara
authors: Ole V
authors: OV
authors: Mortensen
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004553:Electric Conductivity; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D006801:Humans; D008018:Life Cycle Stages / Q000235:genetics; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012550:Schistosoma mansoni / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D012552:Schistosomiasis / Q000188:drug therapy; D012701:Serotonin / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D013379:Substrate Specificity; D014982:Xenopus laevis / Q000235:genetics / Q000378:metabolism / Q000502:physiology
chemical_list: D018076:DNA, Complementary; D020033:Protein Isoforms; D012701:Serotonin; D050486:Serotonin Plasma Membrane Transport Proteins; D017367:Selective Serotonin Reuptake Inhibitors