Study on the construction and function of C-terminal domain recombinant of alanine racemase

Abstract:

[Objective] The N-terminal domain of alanine racemase from Bacillus pseudofirmus OF4 was recombined with the alanine racemase C-terminal domains of many different species to explore the function of C-terminal domain. [Methods] The recombinant genes of alanine racemase were constructed by the gene splicing and expressed in E. coli BL21(DE3). The recombinant proteins were purified by affinity chromatography. D-amino acid oxidase coupling method was used to detect the enzymatic properties of the proteins, while the polymerization states and kinetic parameters of recombinant enzymes were analyzed by the molecular sieve and high-performance liquid chromatography (HPLC). [Results] The recombinant proteins were expressed and purified successfully. OF4TtDadX240c had a catalytic activity which was 60.54% of OF4DadX, whereas other recombinant enzymes lost their activities. The catalytic kinetics showed that the catalytic rate (V_max/K_m) of OF4TtDadX240c decreased about 10-fold, but its stability improved significantly. The half-life of OF4TtDadX240c had about a 5-fold prolongation than OF4DadX, and a significantly improved heat resistance. The results of the molecular sieve showed that OF4DadX, OF4TMDadX226c and OF4TtDadX240c were dimers and other proteins were monomers. However, OF4TMDadX226c lost its activity which could be attributed to the shift of the catalytic active center that failed to form the proton transfer. [Conclusion] The C-terminal folding domain of alanine racemase plays an important role in racemase dimerization, stability and catalytic function.