Molecular mechanism and physiological role of polyamine transport systems and NMDA receptors

点击翻译按钮获取中文摘要

1. N-Methyl-D-aspartate(NMDA)receptors are involved in synaptic plasticity and may also play a role in seizure activity. Overactivation of these receptors can lead to neuronal cell death. Thus, NMDA receptors are potential targets for anticonvulsants and neuroprotective agents. We found that anthraquinone (AQ)- and anthracene (Ant)-tetraamines are potent NMDA channel blockers. The effects of both AQ- and Ant-tetraamines were reversible and voltage-dependent. Results of experiments using mutant NR1 and NR2B subunits of NMDA receptor identified residues that influence block by AQ- and Ant-tetraamines. The results indicate that the polyamine tail is crucial for block by AQ- and Ant-tetraamines. Residues in the outer vestibule of the NR1 subunit were more strongly involved in block by AQ- and Ant-tetraamines than residues in the corresponding region of NR2B.2. CadB, a cadaverine-lysine antiporter, is strongly involved in cell growth under acidic conditions in Escherichia coll. Amino acid residues involved in the activity of CadB were determined by site-directed mutagenesis of the gene. It was found that Cys370 is essential for the activity and was suggested that a hydrophilic cavity is formed by the transmembrane segments II, III, IV, VI, VII, X, XI and XII.3. We have looked for polyamine-preferential uptake proteins in S. cerevisiae. DUR3 catalyzed the uptake of polyamines together with urea, and SAM3 catalyzed the uptake of polyamines together with S-adenosylmethionine, glutamic acid and lysine. Polyamine uptake was greatly decreased in both DUR3- and SAM3-deficient cells. Polyamine stimulation of cell growth of a polyamine requiring mutant was completely inhibited by the disruption of both DUR3 and SAM3. The results indicate that DUR3 and SAM3 are major polyamine uptake proteins in yeast. It was found that DUR3, but not SAM3, was activated by phosphorylation by polyamine transport protein kinase 2.