Peptidyl-puromycin synthesis on polyribosomes from Escherichia coli

Development of a Novel Amplifiable System to Quantify Hydrogen Peroxide in Living Cells

Although many redox signaling molecules are present at low concentrations, typically ranging from micromolar to submicromolar levels, they often play essential roles in a wide range of biological pathways and disease mechanisms. However, accurately measuring low-abundant analytes has been a significant challenge due to the lack of sensitivity and quantitative capability of existing measurement methods. In this study, we introduced a novel chemically induced amplifiable system for quantifying low-abundance redox signaling molecules in living cells. We utilized H2O2 as a proof-of-concept analyte and developed a probe that quantifies cellular peroxide levels by combining the NanoBiT system with androgen receptor dimerization as a reporting mechanism. Our system demonstrated a highly sensitive response to cellular peroxide changes induced both endogenously and exogenously. Furthermore, the system can be adapted for the quantification of other signaling molecules if provided with suitable probing chemistry.

Design of photocaged puromycin for nascent polypeptide release and spatiotemporal monitoring of translation

The antibiotic puromycin, which inhibits protein translation, is used in a broad range of biochemical applications. The synthesis, characterization, and biological applications of NVOC-puromycin, a photocaged derivative that is activated by UV illumination, are presented. The caged compound had no effect either on prokaryotic or eukaryotic translation or on the viability of HEK 293 cells. Furthermore, no significant release of ribosome-bound polypeptide chains was detected in vitro. Upon illumination, cytotoxic activity, in vitro translation inhibition, and polypeptide release triggered by the uncaging of NVOC-puromycin were equivalent to those of the commercial compound. The quantum yield of photolysis was determined to be 1.1±0.2% and the NVOC-puromycin was applied to the detection of newly translated proteins with remarkable spatiotemporal resolution by using two-photon laser excitation, puromycin immunohistochemistry, and imaging in rat hippocampal neurons.

The chiral synthesis and biochemical properties of electron rich phenolic sulfoxide analogs of sparsomycin

A novel route to activated phenolic sulfoxide analogs of sparsomycin has been developed. These analogs display an enhanced "preincubation effect" as inhibitors of peptide-bond formation. This time-dependent component of inhibition, which is postulated to result from an enzyme-mediated Pummerer rearrangement, is the dominant route to inhibition in these activated analogs.

Sulfoxide configuration in sparsomycin determines time-dependent and competitive inhibition of peptidyl transferase

Sparsomycin, ScRs configuration, was the most potent of the four possible stereoisomers as a competitive inhibitor of peptide bond formation. In addition, the configuration of the two chiral centers dictated whether the compound exhibited time- and temperature-dependent inhibition of peptidyl transferase when incubated with polysomes prior to enzyme assay. The data corroborate the thesis that a peptidyl transferase-mediated acylation of the pivotal sulfoxide moiety and subsequent Pummerer rearrangement play a significant role in the inhibitory properties of sparsomycin.

Importance of the hydrophobic sulfoxide substituent on nontoxic analogs of sparsomycin

Nontoxic analogs of sparsomycin were competitive inhibitors of puromycin in the peptidyl transferase assay with Escherichia coli polysomes. The sensitivity of HeLa cells in vitro to the analogs was used as a preliminary index of cellular toxicity. In vitro killing of HeLa cells by this class of compounds correlated well with in vivo 50% lethal doses. The data indicate that modification of the hydrophobic sulfoxide substituent on sparsomycin decreases the toxicity of the molecule for mammalian cells by several hundredfold. Such modifications have less of an effect on the inhibitory activity of the compounds for peptidyl transferase. The differential effects of an analog active against bacterial but not mammalian cells was due to a decreased uptake of the compound by HeLa cells.

Necessity of the sulfoxide moiety for the biochemical and biological properties of an analog of sparsomycin

An analog of the peptidyl transferase inhibitor sparsomycin was a competitive inhibitor (Ki = 1.8 microM) of peptidyl-puromycin synthesis on E. coli polysomes. Preincubation of polysomes with the compound enhanced the degree of inhibition of peptide bond formation. A model for the involvement of a histidine residue in peptidyl transferase activity is presented as a result of our observations which include direct association of [3H] labelled analog with 70S ribosomes. The correct oxidation state of sulfur in the compound was necessary for the "preincubation effect" and entry of the compound into bacterial cells.

Dissociability of free and peptidyl-tRNA bound ribosomes

The influence of peptidyl-tRNA on the dissociation of yeast 80 S ribosomes into subunits was studied. For this purpose temperature-sensitive (ts) suppressor strain of yeast Saccharomyces cervisiae carrying a defect in peptide chain termination was used. It was found that peptidyl-tRNA did not influence the dissociation of ribosomes either at high salt concentration or in the presence of dissociation factor (DF) from yeast. After dissociation of yeast ribosomes in 0.5 M KCl, peptidyl-tRNA remains bound to the 60 S subunit. Some characteristics of the termination process and release of nascent polypeptides from yeast ribosomes are discussed.