We report a one-pot two-step deracemization strategy for aryl-ring-containing secondary alcohols using a dual biocatalytic system that combines an unspecific peroxygenase and an alcohol dehydrogenase. In this approach, unspecific peroxygenase from Agrocybe aegerita (AaeUPO) catalyzes the non-stereoselective oxidation of secondary alcohols to their corresponding ketones. The resulting ketones are subsequently subjected to enantioselective reduction using the secondary alcohol dehydrogenase from Thermoanaerobacter pseudoethanolicus (TeSADH), affording optically active alcohols with high conversion and enantiomeric excesses of up to 99%. By selecting appropriate TeSADH mutants, the system enables the independent, highly enantioselective synthesis of either alcohol enantiomer. Notably, the AaeUPO-catalyzed oxidation proceeds without external cofactors and generates water as the sole byproduct. This work establishes a useful biocatalytic platform for the asymmetric synthesis of enantiopure alcohols. ... Read more

Synchronizing the convergence of the two-oppositely moving DNA replication machineries at specific termination sites is a tightly coordinated process in bacteria. In Escherichia coli, a “replication fork trap” – found within a chromosomal region where forks are allowed to enter but not leave – is set by the protein–DNA roadblock Tus–Ter. The exact sequence of events by which Tus–Ter blocks replisomes approaching from one direction but not the other has been the subject of controversy for many decades. Specific protein–protein interactions between the nonpermissive face of Tus and the approaching helicase were challenged by biochemical and structural studies. These studies show that it is the helicase-induced strand separation that triggers the formation of new Tus–Ter interactions at the nonpermissive face – interactions that result in a highly stable “locked” complex. This controversy recently gained renewed attention as three single-molecule-based studies scrutinized this elusive Tus–Ter mechanism – leading to new findings and refinement of existing models, but also generating new questions. Here, we discuss and compare the findings of each of the single-molecule studies to find their common ground, pinpoint the crucial differences that remain, and push the understanding of this bipartite DNA–protein system further. ... Read more