ParABS systems facilitate chromosome segregation and plasmid partitioning in bacteria and archaea. ParB protein binds centromeric parS DNA sequences and spreads to flanking DNA. We show that ParB is an enzyme that hydrolyzes cytidine triphosphate (CTP) to cytidine diphosphate (CDP). parS DNA stimulates cooperative CTP binding by ParB and CTP hydrolysis. A nucleotide cocrystal structure elucidates the catalytic center of the dimerization-dependent ParB CTPase. Single-molecule imaging and biochemical assays recapitulate features of ParB spreading from parS in the presence but not absence of CTP. These findings suggest that centromeres assemble by self-loading of ParB DNA sliding clamps at parS. ParB CTPase is not related to known nucleotide hydrolases and might be a promising target for developing new classes of antibiotics.

We rationalize the behaviour of protonated merocyanines in water through cross-validation of 1H NMR, UV-Vis and pH measurements, and show their capability to act as reversible photoacids along light/dark cycles can be described by a four-state model.

Positron emission tomography (PET) is used in drug development to assist dose selection and to establish the relationship between blood and tissue pharmacokinetics (PKs). We present a new biomathematical approach that allows prediction of repeat-dose (RD) brain target occupancy (TO) using occupancy data obtained after administration of a single dose (SD). A PET study incorporating a sequential adaptive design was conducted in 10 healthy male adults who underwent 4 PET scans with [(11)C]DASB ([(11)C]N,N-dimethyl-2-(2-amino-4-cyanophenylthio) benzylamine): 1 at baseline, 2 after 20 mg SD of the 5-hydroxytryptamine transporter (5-HTT) inhibitor duloxetine, and 1 after 4 days daily administration of 20 mg duloxetine. An adaptive design was used to select optimal times after SD for measurement of occupancy. Both direct and indirect PK/TO models were fitted to the SD data to characterise the model parameters and then applied to a predicted RD duloxetine plasma time course to predict the 5-HTT occupancy after RD. Repeat-dose prediction from the indirect model (OC(50)=2.62±0.93 ng/mL) was significantly better (P<0.05) than that from the direct model (OC(50)=2.29±1.11 ng/mL). This approach increases the value of SD occupancy studies that are performed as part of first time in human drug development programmes by providing an estimate of the dose required to achieve the desired TO at RD.

The data demonstrate the sleep-promoting properties of the orexin antagonist SB-649868 in male patients with insomnia.