title: Large scale production of the active human ASCT2 (SLC1A5) transporter in Pichia pastoris--functional and kinetic asymmetry revealed in proteoliposomes.
abstract: The human glutamine/neutral amino acid transporter ASCT2 (hASCT2) was over-expressed in Pichia pastoris and purified by Ni(2+)-chelating and gel filtration chromatography. The purified protein was reconstituted in liposomes by detergent removal with a batch-wise procedure. Time dependent [(3)H]glutamine/glutamine antiport was measured in proteoliposomes which was active only in the presence of external Na(+). Internal Na(+) slightly stimulated the antiport. Optimal activity was found at pH7.0. A substantial inhibition of the transport was observed by Cys, Thr, Ser, Ala, Asn and Met (≥70%) and by mercurials and methanethiosulfonates (≥80%). Heterologous antiport of [(3)H]glutamine with other neutral amino acids was also studied. The transporter showed asymmetric specificity for amino acids: Ala, Cys, Val, Met were only inwardly transported, while Gln, Ser, Asn, and Thr were transported bi-directionally. From kinetic analysis of [(3)H]glutamine/glutamine antiport Km values of 0.097 and 1.8mM were measured on the external and internal sides of proteoliposomes, respectively. The Km for Na(+) on the external side was 32mM. The homology structural model of the hASCT2 protein was built using the GltPh of Pyrococcus horikoshii as template. Cys395 was the only Cys residue externally exposed, thus being the potential target of SH reagents inhibition and, hence, potentially involved in the transport mechanism.
authors.affiliation: Department BEST (Biologia, Ecologia, Scienze della Terra) Unit of Biochemistry and Molecular Biotechnology, University of Calabria, Via P. Bucci 4c, 87036 Arcavacata di Rende, Italy. piero.pingitore@alice.it
authors.forename: Piero
authors.initials: P
authors.lastname: Pingitore
authors.forename: Lorena
authors.initials: L
authors.lastname: Pochini
authors.forename: Mariafrancesca
authors.initials: M
authors.lastname: Scalise
authors.forename: Michele
authors.initials: M
authors.lastname: Galluccio
authors.forename: Kristina
authors.initials: K
authors.lastname: Hedfalk
authors.forename: Cesare
authors.initials: C
authors.lastname: Indiveri
mesh_terms: D026962:Amino Acid Transport System ASC / Q000737:chemistry* / Q000235:genetics; D001692:Biological Transport; D003001:Cloning, Molecular; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D015870:Gene Expression; D005973:Glutamine / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D017669:Mercury Compounds / Q000737:chemistry; D008698:Mesylates / Q000737:chemistry; D015778:Minor Histocompatibility Antigens; D008958:Models, Molecular; D010843:Pichia / Q000235:genetics*; D011510:Proteolipids / Q000737:chemistry* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D026962:Amino Acid Transport System ASC; D017669:Mercury Compounds; D008698:Mesylates; D015778:Minor Histocompatibility Antigens; D011510:Proteolipids; C420506:SLC1A5 protein, human; C020485:proteoliposomes; D005973:Glutamine; C074502:methanethiosulfonate; D003545:Cysteine
keywords: 2-(trimethylammonium)ethyl methanethiosulfonate, Bromide; 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid; 2-aminoethyl methanethiosulfonate hydrobromide; 3-((3-cholamidopropyl)dimethylammonium)-1-propanesulfonate; BCH; BMGY; Buffered Glycerol-complex Medium; C(12)E(8); CHAPS; DDM; DEPC; LDAO; Liposomes; MTSEA; MTSET; MeAIB; N-ethylmaleimide; N-phenylmaleimide; NEM; Over-expression; PEM; PLP; Purification; Transport; YPDS; Yeast Extract Peptone Dextrose Sorbitol; a-(methylamino)isobutyric acid; diethyl pyrocarbonate; n-dodecyl-N,N-dimethylamine-N-oxide; n-dodecyl-beta-D-maltoside; octaethylene glycol monododecyl ether; p-OHMB; p-hydroxymercuribenzoate; pyridoxal-5-phosphate