Subunit fusion of two yeast D-amino acid oxidases enhances their thermostability and resistance to H2O2.

D-amino acid oxidases from Rhodosporidium toruloides and Trigonopsis variabilis (RtDAO and TvDAO) are both yeast homodimeric flavoenzymes. Two of their cDNA genes were connected by a hexanucleotide linker and heterologously expressed in E. coli to produce the corresponding double DAOs (dRtDAO and dTvDAO) with two subunits fused into a single polypeptide. The specific activities of double DAOs remained similar to those of native dimeric DAOs, although the catalytic efficiencies (k(cat)/K(M)) were decreased due to higher K(M) values. The T(m) value for dRtDAO was shifted 5 degrees C higher while that for dTvDAO was increased only by 2 degrees C, in comparison with the corresponding native counterparts. In the presence of 10 mM H(2)O(2), dRtDAO and dTvDAO exhibited half-lives of about 60 and 40 min, respectively, which were 2- and 1.5-fold, respectively, longer than their native DAOs. These yeast DAOs can therefore be thermally and oxidatively stabilized by linking their subunits together.