title: Aquaporin AqpZ is involved in cell volume regulation and sensitivity to osmotic stress in Synechocystis sp. strain PCC 6803.
abstract: The moderately halotolerant cyanobacterium Synechocystis sp. strain PCC 6803 contains a plasma membrane aquaporin, AqpZ. We previously reported that AqpZ plays a role in glucose metabolism under photomixotrophic growth conditions, suggesting involvement of AqpZ in cytosolic osmolarity homeostasis. To further elucidate the physiological role of AqpZ, we have studied its gene expression profile and its function in Synechocystis. The expression level of aqpZ was regulated by the circadian clock. AqpZ activity was insensitive to mercury in Xenopus oocytes and in Synechocystis, indicating that the AqpZ can be categorized as a mercury-insensitive aquaporin. Stopped-flow light-scattering spectrophotometry showed that addition of sorbitol and NaCl led to a slower decrease in cell volume of the Synechocystis ΔaqpZ strain than the wild type. The ΔaqpZ cells were more tolerant to hyperosmotic shock by sorbitol than the wild type. Consistent with this, recovery of oxygen evolution after a hyperosmotic shock by sorbitol was faster in the ΔaqpZ strain than in the wild type. In contrast, NaCl stress had only a small effect on oxygen evolution. The amount of AqpZ protein remained unchanged by the addition of sorbitol but decreased after addition of NaCl. This decrease is likely to be a mechanism to alleviate the effects of high salinity on the cells. Our results indicate that Synechocystis AqpZ functions as a water transport system that responds to daily oscillations of intracellular osmolarity.
authors.affiliation: Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aobayama, Sendai, Japan.
authors.forename: Masaro
authors.initials: M
authors.lastname: Akai
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Onai
authors.forename: Megumi
authors.initials: M
authors.lastname: Morishita
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Mino
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Shijuku
authors.forename: Hisataka
authors.initials: H
authors.lastname: Maruyama
authors.forename: Fumihito
authors.initials: F
authors.lastname: Arai
authors.forename: Shigeru
authors.initials: S
authors.lastname: Itoh
authors.forename: Akihiro
authors.initials: A
authors.lastname: Hazama
authors.forename: Vanessa
authors.initials: V
authors.lastname: Checchetto
authors.forename: Ildikò
authors.initials: I
authors.lastname: Szabò
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Yukutake
authors.forename: Makoto
authors.initials: M
authors.lastname: Suematsu
authors.forename: Masato
authors.initials: M
authors.lastname: Yasui
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ishiura
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Uozumi
mesh_terms: D020346:Aquaporins / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport / Q000235:genetics; D048429:Cell Size; D057906:Circadian Clocks; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D008627:Mercuric Chloride / Q000494:pharmacology; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D010100:Oxygen / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D013012:Sorbitol / Q000494:pharmacology; D046939:Synechocystis / Q000235:genetics / Q000502:physiology*; D014867:Water / Q000378:metabolism
chemical_list: D020346:Aquaporins; D001426:Bacterial Proteins; D014867:Water; D012965:Sodium Chloride; D013012:Sorbitol; D008627:Mercuric Chloride; D010100:Oxygen