Characterization of an atypical, thermostable, organic solvent- and acid-tolerant 2′-deoxyribosyltransferase from Chroococcidiopsis thermalis

In our search for thermophilic and acid-tolerant nucleoside 2′-deoxyribosyltransferases (NDTs), we found a good candidate in an enzyme encoded by Chroococcidiopsis thermalis PCC 7203 (CtNDT). Biophysical and biochemical characterization revealed CtNDT as a homotetramer endowed with good activity and stability at both high temperatures (50–100 °C) and a wide range of pH values (from 3 to 7). CtNDT recognizes purine bases and their corresponding 2′-deoxynucleosides but is also proficient using cytosine and 2′-deoxycytidine as substrates. These unusual features preclude the strict classification of CtNDT as either a type I or a type II NDT and further suggest that this simple subdivision may need to be updated in the future. Our findings also hint at a possible link between oligomeric state and NDT’s substrate specificity. Interestingly from a practical perspective, CtNDT displays high activity (80–100%) in the presence of several water-miscible co-solvents in a proportion of up to 20% and was successfully employed in the enzymatic production of several therapeutic nucleosides such as didanosine, vidarabine, and cytarabine.