Bacillus subtilis YtpP and Thioredoxin A Are New Players in the Coenzyme-A-Mediated Defense Mechanism against Cellular Stress

Coenzyme A (CoA) is an important cellular metabolite that is critical for metabolic processes and the regulation of gene expression. Recent discovery of the antioxidant function of CoA has highlighted its protective role that leads to the formation of a mixed disulfide bond with protein cysteines, which is termed protein CoAlation. To date, more than 2000 CoAlated bacterial and mammalian proteins have been identified in cellular responses to oxidative stress, with the majority being involved in metabolic pathways (60%). Studies have shown that protein CoAlation is a widespread post-translational modification which modulates the activity and conformation of the modified proteins. The induction of protein CoAlation by oxidative stress was found to be rapidly reversed after the removal of oxidizing agents from the medium of cultured cells. In this study, we developed an enzyme-linked immunosorbent assay (ELISA)-based deCoAlation assay to detect deCoAlation activity from Bacillus subtilis and Bacillus megaterium lysates. We then used a combination of ELISA-based assay and purification strategies to show that deCoAlation is an enzyme-driven mechanism. Using mass-spectrometry and deCoAlation assays, we identified B. subtilis YtpP (thioredoxin-like protein) and thioredoxin A (TrxA) as enzymes that can remove CoA from different substrates. With mutagenesis studies, we identified YtpP and TrxA catalytic cysteine residues and proposed a possible deCoAlation mechanism for CoAlated methionine sulfoxide reducatse A (MsrA) and peroxiredoxin 5 (PRDX5) proteins, which results in the release of both CoA and the reduced form of MsrA or PRDX5. Overall, this paper reveals the deCoAlation activity of YtpP and TrxA and opens doors to future studies on the CoA-mediated redox regulation of CoAlated proteins under various cellular stress conditions.

The influence of multiple oral administration on the pharmacokinetics and distribution profile of dalcetrapib in rats

We investigated the influence of multiple oral administration on the accumulation of dalcetrapib (JTT-705/RO4607381), a novel cholesteryl ester transfer protein inhibitor, in rats. It is well known that orally administered dalcetrapib is rapidly hydrolysed to its active form, which has a sulfhydryl group, in the body. The active form then binds covalently to endogenous thiols via mixed disulfide bonds. Following multiple once daily oral administration of ¹⁴C-dalcetrapib for seven days to rats, the concentration of radioactivity in the plasma and almost all tissues reached the steady state by day 4. At 24 h after the last dose, there was a relatively high concentration of radioactivity in the mesenteric lymph nodes, liver, adrenal glands and fat. After the last dose to rats, the radioactivity was almost completely recovered in the urine and faeces, indicating that dalcetrapib is not retained in the body, probably due to the reversibility of the disulfide bonds despite being covalent bonds.

Intrinsic site-selectivity of ubiquitin dimer formation

The post-translational modification of proteins with ubiquitin can take on many forms, including the decoration of substrates with polymeric ubiquitin chains. These chains are linked through one of the seven lysine residues in ubiquitin, with the potential to form a panoply of linkage combinations as the chain length increases. The ensuing structural diversity of modifications serves a variety of signaling functions. Still, some linkages are present at a much higher level than others in cellulo. Although ubiquitination is an enzyme-catalyzed process, the large disparity of abundancies led us to the hypothesis that some linkages might be intrinsically faster to form than others, perhaps directing the course of enzyme evolution. Herein, we assess the kinetics of ubiquitin dimer formation in an enzyme-free system by measuring the rate constants for thiol-disulfide interchange between appropriate ubiquitin variants. Remarkably, we find that the kinetically expedient linkages correlate with those that are most abundant in cellulo. As the abundant linkages also appear to function more broadly in cellulo, this correlation suggests that the more accessible chains were selected for global roles.

Pharmacokinetics and disposition of dalcetrapib in rats and monkeys

1. The pharmacokinetics and metabolism of dalcetrapib (JTT-705/RO4607381), a novel cholesteryl ester transfer protein inhibitor, were investigated in rats and monkeys. 2. In in vitro stability studies, dalcetrapib was extremely unstable in plasma, liver S9 and small intestinal mucosa, and the pharmacologically active form (dalcetrapib thiol) was detected as major component. Most of the active form in plasma was covalently bound to plasma proteins via mixed disulfide bond formation. 3. Following oral administration of (14)C-dalcetrapib to rats and monkeys, active form was detected in plasma. The active form was mainly metabolized to the glucuronide conjugate and the methyl conjugate at the thiol group. Several minor metabolites including mono- and di-oxidized forms of the glucuronide are also detected in the plasma and urine. 4. The administered radioactivity was widely distributed to all tissues and mainly excreted into the feces (85.7 and 62.7% of the dose in rats and monkeys, respectively). Most of the radioactivity was recovered by 168 h. Although the absorbed dalcetrapib was hydrolyzed to the active form and was bound to endogenous thiol via formation of disulfide bond, it was relatively rapidly eliminated from the body and was not retained.