OleD is shown to play a key reductive role in the generation of alkenes (olefins) from acyl thioesters in Stenotrophomonas maltophilia. The gene coding for OleD clusters with three other genes, oleABC, and all appear to be transcribed in the same direction as an operon in various olefin producing bacteria. In this study, a series of substrates varying in chain length and stereochemistry were synthesized and used to elucidate the functional role and substrate specificity of OleD. We demonstrated that OleD, which is an NADP(H) dependent reductase, is a homodimer which catalyzes the reversible stereospecific reduction of 2-alkyl-3-ketoalkanoic acids. Maximal catalytic efficiency was observed with syn-2-decyl-3-hydroxytetradecanoic acid, with a k(cat)/K(m) 5- and 8-fold higher than for syn-2-octyl-3-hydroxydodecanoic acid and syn-2-hexyl-3-hydroxydecanoic acid, respectively. OleD activity was not observed with syn-2-butyl-3-hydroxyoctanoic acid and compounds lacking a 2-alkyl group such as 3-ketodecanoic and 3-hydroxydecanoic acids, suggesting the necessity of the 2-alkyl chain for enzyme recognition and catalysis. Using diastereomeric pairs of substrates and 4 enantiopure isomers of 2-hexyl-3-hydroxydecanoic acid of known stereochemistry, OleD was shown to have a marked stereochemical preference for the (2R,3S)-isomer. Finally, experiments involving OleA and OleD demonstrate the first 3 steps and stereochemical course in olefin formation from acyl thioesters; condensation to form a 2-alkyl-3-ketoacyl thioester, subsequent thioester hydrolysis, and ketone reduction.

Single-cell omics provide insight into cellular heterogeneity and function. Recent technological advances have accelerated single-cell analyses, but workflows remain expensive and complex. We present a method enabling simultaneous, ultra-high throughput single-cell barcoding of millions of cells for targeted analysis of proteins and RNAs. Quantum barcoding (QBC) avoids isolation of single cells by building cell-specific oligo barcodes dynamically within each cell. With minimal instrumentation (four 96-well plates and a multichannel pipette), cell-specific codes are added to each tagged molecule within cells through sequential rounds of classical split-pool synthesis. Here we show the utility of this technology in mouse and human model systems for as many as 50 antibodies to targeted proteins and, separately, >70 targeted RNA regions. We demonstrate that this method can be applied to multi-modal protein and RNA analyses. It can be scaled by expansion of the split-pool process and effectively renders sequencing instruments as versatile multi-parameter flow cytometers.

In the original published version of the article, the name of co-author Samuel Higgins was spelled incorrectly. In addition, there were minor errors in Figures 2, 3, 4, 7, and 8 that affected the clarity of the presented information. The errors have been corrected in the HTML and PDF versions of the paper.

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