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J. Biochem, 2003, Vol. 133, No. 2 173-180
© 2003 Japanese Biochemical Society

BIOCHEMISTRY

A Novel Neutral Amino Acid Transporter from the Hyperthermophilic Archaeon Thermococcus sp. KS-1

Shohei Akahane, Hideaki Kamata, Hitoshi Yagisawa and Hajime Hirata+,

Department of Life Science, Graduate School of Science, Himeji Institute of Technology, Hyogo 678-1297

A novel gene encoding a small neutral amino acid transporter was cloned from the genome of the hyperthermophilic archaeon Thermococcus sp. KS-1 by functional cloning using Escherichia coli strain AK430, which is defective in transporting glycine and D-alanine. The cloned gene, snatA, encoded a protein of 216 amino acid residues, SnatA, and was predicted to be a membrane protein with six membrane-spanning segments. E. coli AK430 cells transformed with snatA transported glycine with an apparent Kt value of 24 µM, which was one order of magnitude higher than that of other known glycine/alanine transporters, including cycA of E. coli and acp of thermophilic bacterium PS3. Competition studies revealed that SnatA transported various L-type neutral amino acids, but its substrate specificity was different from that of CycA or ACP. The glycine transport was inhibited by a protonophore, FCCP, or valinomycin plus nigericin, indicating that the process is dependent on an electrochemical potential of H+. Homology searches revealed no homology with any transporters known to date. However, several hypothetical genes in prokaryote cells enrolled in the gene bank showed significantly high homology scores, indicating that snatA and its homologues form a family of prokaryotes. To our knowledge, this is the first report on the cloning of a gene of an amino acid transporter from a hyperthermophilic archaeon.

+ To whom correspondence should be addressed. Tel: +81-791-58-0205, Fax: +81-791-58-0198, E-mail: hirata{at}sci.himeji-tech.ac.jp


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