Na+-dependent K+ uptake Ktr system from the cyanobacterium Synechocystis sp. PCC 6803 and its role in the early phases of cell adaptation to hyperosmotic shock

Nobuyuki Matsuda, Hiroshi Kobayashi, Hirokazu Katoh, Teruo Ogawa, Lui Futatsugi, Tatsunosuke Nakamura, Evert P. Bakker, Nobuyuki Uozumi

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70 Citations (Scopus)

Abstract

Transmembrane ion transport processes play a key role in the adaptation of cells to hyperosmotic conditions. Previous work has shown that the disruption of a ktrB/ntpJ-Wse putative Na+TK+ transporter gene in the cyanobacterium Synechocystis sp. PCC 6803 confers increased Na+ sensitivity, and inhibits HCO3- uptake. Here, we report on the mechanistic basis of this effect. Heterologous expression experiments in Escherichia coli show that three Synechocystis genes are required for K + transport activity. They encode an NAD+-binding peripheral membrane protein (ktrA; sll0493), an integral membrane protein, belonging to a superfamily of K+ transporters (ktrB; formerly ntpJ; slr1509), and a novel type of kfr gene product, not previously found in Ktr systems (ktrE; slr1508). In E. coli, Synechocystis KtrABE-mediated K+ uptake occurred with a moderately high affinity (Km of about 60 μM), and depended on both Na+ and a high membrane potential, but not on ATP. KtrABE neither mediated Na+ uptake nor Na+ efflux. In Synechocystis sp. PCC 6803, KtrB-mediated K+ uptake required Na+ and was inhibited by protonophore. A ΔktrB strain was sensitive to long term hyperosmotic stress elicited by either NaCl or sorbitol. Hyperosmotic shock led initially to loss of net K+ from the cells. The ΔktrB cells shocked with sorbitol failed to reaccumulate K+ up to its original level. These data indicate that in strain PCC 6803 K+ uptake via KtrABE plays a crucial role in the early phase of cell turgor regulation after hyperosmotic shock.

Original languageEnglish
Pages (from-to)54952-54962
Number of pages11
JournalJournal of Biological Chemistry
Volume279
Issue number52
DOIs
Publication statusPublished - 2004 Dec 24

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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