We describe the application of a novel eosin Y (EY)-derived polymer photocatalyst for the synthesis of polymeric bioconjugates. The photocatalyst, a copolymer of eosin Y acrylate and N-isopropylacrylamide, can induce light-mediated reversible-deactivation radical polymerization in biologically benign conditions. Heating the reaction mixture to 37 °C causes precipitation of the photocatalyst in a hydrophilic-to-hydrophobic transition, allowing for simple purification of the polymer–protein conjugates via filtration without compromising enzyme activity. We discuss the optimization of the polymerization conditions for imparting control over molecular weight and reaction kinetics and demonstrate the recyclability of the recovered photocatalyst. Overall, this strategy will advance bioconjugate manufacturing through facilitated purification and improved sustainability.

Mycobacterium abscessus (Mab) causes serious infections that often require over 18 months of antibiotic combination therapy. There is no standard regimen for the treatment of Mab infections and the multitude of combinations that have been used clinically have had low success rates and high rates for toxicities. With β-lactam antibiotics being safe, double β-lactam and β-lactam/β-lactamase inhibitor combinations are of interest for improving treatment of Mab infections and minimizing toxicity. However, a mechanistic approach for building these combinations is lacking since little is known about which penicillin-binding protein (PBP) target receptors are inactivated by different β-lactams in Mab. We determined the preferred PBP targets of 13 β-lactams and two β-lactamase inhibitors in two Mab strains and identified PBP sequences by proteomics. The Bocillin FL binding assay was used to determine the β-lactam concentrations (IC50) that half-maximally inhibited Bocillin binding. Principal component analysis identified four clusters of PBP occupancy patterns. Carbapenems inactivated all PBPs at low concentrations (0.016-0.5mg/L; cluster 1). Cephalosporins (cluster 2) inactivated PonA2, PonA1, and PbpA at low (0.031-1mg/L; ceftriaxone and cefotaxime) or intermediate concentrations (0.35-16mg/L; ceftazidime and cefoxitin). Sulbactam, aztreonam, carumonam, mecillinam and avibactam (cluster 3) inactivated the same PBPs as cephalosporins, but required higher concentrations. Other penicillins (cluster 4) specifically targeted PbpA at 2-16mg/L. Carbapenems, ceftriaxone and cefotaxime were the most promising β-lactams since they inactivated most or all PBPs at clinically relevant concentrations. These first PBP occupancy patterns in Mab provide a mechanistic foundation for selecting and optimizing safe and effective combination therapies with β-lactams.

PROteolysis Targeting Chimeras (PROTACs) are bifunctional molecules that degrade target proteins through recruiting E3 ligases. However, their application is limited in part because few E3 ligases can be recruited by known E3 ligase ligands. Through competitive activity-based protein profiling, we found that piperlongumine (PL), a natural product, binds multiple E3 ligases. To evaluate whether PL can be used as an E3 ligase ligand, we generated a series of PL and SNS-032 (a selective CDK9 inhibitor) conjugates and found that the lead conjugate 955 can potently degrade CDK9 in a ubiquitin-proteasome dependent manner. In addition, 955 is more potent than SNS-032 against various tumor cells in vitro. Through TurboID-based proteomics and mechanistic studies, we identified KEAP1 as the E3 ligase recruited by PL to degrade CDK9. These findings demonstrate that PL is a novel E3 ligase ligand that can be used to generate potent anticancer PROTACs.

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Extracellular membrane vesicles (EMVs) are produced by many Gram-positive organisms, but information regarding vesiculogenesis is incomplete. We used single gene deletions to evaluate the impacts on Streptococcus mutans EMV biogenesis of Sortase A (SrtA), which affects S. mutans EMV composition, and Sfp, a 4phosphopantetheinyl transferase that affects Bacillus subtilis EMV stability. srtA EMVs were notably larger than sfp and wild-type (WT) EMVs. EMV proteins identified from all three strains are known to be involved in cell wall biogenesis and cell architecture, bacterial adhesion, biofilm cell density and matrix development, and microbial competition. Notably, the AtlA autolysin was not processed to its mature active form in the srtA mutant. Proteomic and lipidomic analyses of all three strains revealed multiple dissimilarities between vesicular and corresponding cytoplasmic membranes (CMs). A higher proportion of EMV proteins are predicted substrates of the general secretion pathway (GSP). Accordingly, the GSP component SecA was identified as a prominent EMV-associated protein. In contrast, CMs contained more multi-pass transmembrane (TM) protein substrates of co-translational transport machineries than EMVs. EMVs from the WT, but not the mutant strains, were enriched in cardiolipin compared to CMs, and all EMVs were over-represented in polyketide flavonoids. EMVs and CMs were rich in long-chain saturated, monounsaturated, and polyunsaturated fatty acids, except for sfp EMVs that contained exclusively polyunsaturated fatty acids. Lipoproteins were less prevalent in EMVs of all three strains compared to their CMs. This study provides insight into biophysical characteristics of S. mutans EMVs and indicates discrete partitioning of protein and lipid components between EMVs and corresponding CMs of WT, srtA, and sfp strains.