2′-Deoxyribosyltransferase from Bacillus psychrosaccharolyticus: A Mesophilic-Like Biocatalyst for the Synthesis of Modified Nucleosides from a Psychrotolerant Bacterium

Structure-function relationships of a novel 2-deoxyribosyltransferase from the psychrotolerant bacterium Bacillus psychrosaccharolyticus (BpNDT) have been exhaustively studied by biochemical and high resolution crystallographic analyses. Despite BpNDT exhibiting some structural features characteristic of cold-adapted enzymes such as localized flexibility in critical loops, its biochemical properties are typical of mesophilic enzymes. BpNDT is a highly symmetrical homohexamer with tightly associated subunits that possesses flexible and short loops bordering the active sites. The catalytic center is essentially identical to that of other mesophilic homologues. Moreover, BpNDT shows that it is a mesophilic-like enzyme since it is not heat-labile and exhibits an apparent unfolding temperature (T-m) of 49 degrees C, being active during 96 h at 40 and 50 degrees C. Finally, BpNDT synthesizes natural and modified nucleosides, with preference for purines as acceptors and pyrimidine nucleosides as donors. Remarkably, the synthesis of several therapeutic nucleosides has been efficiently carried out. In this sense, 5-hydroxymethyl-2-deoxyuridine (5-HMdUrd), 7-deaza-6-hydroxypurine-2-deoxyriboside (7-DHPdRib) and theophylline-2-deoxyriboside were synthesized for the first time by an NDT enzyme, showing the biotechnological interest of BpNDT.