2Department of Veterinary Technology, Faculty of Veterinary Technology, Kasetsart University, Bangkok, 10900, Thailand
3Department of Biosciences, Åbo Akademi University, FI20520 Turku, Finland
4Department of Biochemistry and Food Chemistry, Laboratory of Molecular Plant Biology, University of Turku, FI20014 Turku, Finland
* To whom correspondence should be addressed.
Received January 19, 2011; Revision received February 7, 2011
His-tagged Synechocystis sp. PCC 6803 PotD protein (rPotD) involved in polyamine transport was overexpressed in Escherichia coli. The purified rPotD showed saturable binding kinetics with radioactively labeled polyamines. The rPotD exhibited a similar binding characteristic for three polyamines, with putrescine having less preference. The Kd values for putrescine, spermine, and spermidine were 13.2, 8.3, and 7.8 µM, respectively. Binding of rPotD with polyamines was maximal at pH 8.0. Docking of these polyamines into the homology model of Synechocystis PotD showed that all three polyamines are able to interact with Synechocystis PotD. The binding modes of the docked putrescine and spermidine in Synechocystis are similar to those of PotF and PotD in E. coli, respectively. Competition experiments showed specific binding of rPotD with polyamines. The presence of putrescine and spermidine in the growth medium could induce an increase in PotD contents, suggesting the role of PotD in mediating the transport of polyamine in Synechocystis sp. PCC 6803.
KEY WORDS: polyamine binding, polyamine docking, PotD induction, rPotD, Synechocystis sp. PCC 6803