Tat-mediated protein transduction of human brain pyridoxine-5-P oxidase into PC12 cells.
Pyridoxine-5-P oxidase catalyses the terminal step in the biosynthesis of pyridoxal-5-P, the biologically active form of vitamin B6 which acts as an essential cofactor. Here, a human brain pyridoxine-5-P oxidase gene was fused with a gene fragment encoding the HIV-1 Tat protein transduction domain (RKKRRQRRR) in a bacterial expression vector to produce a genetic in-frame Tat-pyridoxine-5-P oxidase fusion protein. Expressed and purified Tat-pyridoxine-5-P oxidase fusion protein transduced efficiently into PC12 cells in a time- and dose-dependent manner when added exogenously to culture media. Once inside the cells, the transduced Tat-pyridoxine-5-P oxidase protein showed catalytic activity and was stable for 48 h. Moreover, the formation of pyridoxal-5-P was increased by adding exogenous Tat-pyridoxine-5-P oxidase to media pre-treated with the vitamin B6 precursor pyridoxine. In addition, the intracellular concentration of pyridoxal-5-P was markedly increased when Tat-pyridoxal kinase was transduced together with Tat-pyridoxine-5-P oxidase into cells.These results suggest that the transduction of Tat-pyridoxine-5-P oxidase fusion protein presents a means of regulating the level of pyridoxal-5-P and of replenishing this enzyme in various neurological disorders related to vitamin B6.