Structure-function relationships of porcine pyridoxal kinase

Pyridoxal kinase (PK) catalyzes the formation of pyridoxal-5-phosphate (PLP) from pyridoxal (PL), ATP and a divalent cation (Zn2+). So far, there is no three-dimensional structure of PK available. Site-directed mutagenesis was carried out to study the importance of three conserved residues: Tyr137, Gly242 and Gly244. The mutants (Y137F, G242A and G244A) were constructed, expressed, purified and analyzed. The results demonstrated that the mutants had much less activity but with no dramatic variation in protein stability. Tyr137 residue was shown to be involved in PL binding but not ATP binding. For the G244A mutant, the absence of enzyme activity was probably due to the deficiency in PL binding rather than the lack of ATP binding. In the case of the G242A mutant, it did not bind to ATP or FL.