Enhancing the expression of terminal deoxynucleotidyl transferases by N-terminal truncation

Terminal deoxynucleotidyl transferase (TdT), a unique DNA polymerase that catalyzes the template-free incorporation of nucleotides into single-stranded DNA, has facilitated the development of various oligonucleotide-based tools and methods, especially in the field of template-free enzymatic DNA synthesis. However, expressing vertebrate-derived TdTs in Escherichia coli complicates purification and increases production costs. In this study, N-terminal truncation of TdTs was performed to improve their expression and stability. The results revealed that N-terminal truncation could enhance the expression level of six TdTs. Among the truncated mutants, N-140-ZaTdT and N-140-CpTdT, with 140 amino acids removed, exhibited an increase in protein expression, which was 9.5- and 23-fold higher than their wild-types, respectively. Importantly, the truncation preserves the catalytic function of TdT. Additionally, the T_m values of N-140-ZaTdT increased by 4.9°C. The improved expression of the truncated mutants makes them more suitable for reducing production costs and advancing enzyme engineering.