TY - JOUR
T1 - 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
AU - Matsuda, Nobuyuki
AU - Kobayashi, Hiroshi
AU - Katoh, Hirokazu
AU - Ogawa, Teruo
AU - Futatsugi, Lui
AU - Nakamura, Tatsunosuke
AU - Bakker, Evert P.
AU - Uozumi, Nobuyuki
PY - 2004/12/24
Y1 - 2004/12/24
N2 - 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.
AB - 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.
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U2 - 10.1074/jbc.M407268200
DO - 10.1074/jbc.M407268200
M3 - Article
C2 - 15459199
AN - SCOPUS:11144226383
VL - 279
SP - 54952
EP - 54962
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
SN - 0021-9258
IS - 52
ER -