Poster: Membrane Transport

Abs # 1215: Functional analysis of K⁺ transporter Ktr from Synechocystis sp. PCC6803

Presenter:	Matsuda, Nobuyuki , mattasi@mail.goo.ne.jp
Authors	Matsuda, Nobuyuki  (A)   Kobayashi, Hiroshi  (B)   Nakamura, Tatsunosuke  (C)   Bakker, Evert P. (D)   Katoh, Hirokazu  (E)   Ogawa, Teruo  (E)   Uozumi, Nobuyuki  (A) (E)
Affiliations:	(A): Grad. Sch. Bioagr., Nagoya Univ., Nagoya 464-8601 (B): Fac. Pharmaceutical Sci., Chiba Univ., Chiba 263-0022 (C): Fac. of Pharmacy, Niigata Univ. of Parmacy and Applied Life Sci., Niigata 950-2081 (D): Dept of Microbiology., Univ. Osnabruck, Osnabruck D-49069 (E): Bioscience Center, Nagoya Univ., Nagoya 464-8601

Potassium ion (K⁺) is the major cation in the cytoplasm of all cell types. It is supplied from the medium by transport across the cytoplasmic membrane via different types of systems. Bacteria and plants contain both K⁺ transporters and K⁺ channels, which play a role in a variety of environmental responses and in signal transduction. The homologous genes of K⁺ transporters and K⁺ channels have been isolated from many organisms, and their structure and function have been studied to date. In this study, we have isolated from the cyanobacterium Synechocystis sp. PCC6803 the gene encoding the protein, SynKtrB, which shares homology with both plant Na⁺/K⁺ transporter (HKT family) and bacterial K⁺ transporter (Ktr/Trk family). It was found that the wild-type cyanobacteria Synechocystis sp. PCC6803 possesses K⁺ transport activity, but the Synechocystis mutant disrupted in the SynKtr gene does not show K⁺ transport activity. It has been reported that the Synechocystis mutant could not grow in the high salinity medium. When the SynKtr protein was expressed in K⁺ uptake deficient E. coli strain LB2003 (Dtrk, Dkdp, kup1), this strain grew in a low potassium medium, and K⁺ transport activity was detected by the measurement of K⁺ uptake using flame photometry. We also found that Na⁺ activated this K⁺ uptake transport, although the SynKtr transporter did not exhibit detectable Na⁺ transport activity. Moreover the K⁺ transport activity was impaired by addition of the protonophore CCCP in the E. coli expression system, suggesting that K⁺ transport via the SynKtr transporter depends on the proton motive force.