Biology subjects

Lehman, S. M.

Publications and source records attributed to Lehman, S. M..

3 recordsLinked to original sources

bioRxiv2025

Optimizing phage-antibiotic combinations: impact of administration order against daptomycin non-susceptible (DNS) MRSA clinical isolates

BackgroundThe rise of bacterial resistance has driven the exploration of novel therapies, such as bacteriophage-antibiotic cocktails (PACs), which have shown in vitro promise against resistant pathogens, including daptomycin non-susceptible (DNS-MRSA) strains. While daptomycin has been a cornerstone for treating MRSA bacteremia and vancomycin-refractory infective endocarditis, the emergence of DNS-MRSA presents a significant challenge due to high morbidity, mortality, and rapid intrinsic resistance development. MethodsPhages Intesti13 and Sb-1, were selected for their unique host ranges and activity against sixteen DNS-MRSA strains. Synergy with antibiotics was assessed via growth suppression curves and 24-hour time-kill assays (TKAs) across administration sequences and MIC increments. Selected regimens were further assessed in an ex-vivo simulated endocardial vegetation (SEV) models, with pharmacokinetic analyses confirming target antibiotic concentrations. ResultsIn the ex-vivo SEV model, simultaneous PAC administration using daptomycin{+/-}phage, showed superior bactericidal activity over sequential treatments in isolate C6 (p<0.01). Similarly, in the same model, C2 reached detection limits within 48h and remained suppressed for 120h (p<0.0037). Sequential outcomes varied by phage-antibiotic order and antibiotic choice. Simultaneous and phage-first regimens outperformed antibiotic-first, especially in 24h TKAs, but showed variability at lower MICs and between in-vitro and ex-vivo settings. ConclusionThis study highlights PACs potential for DNS-MRSA treatment, emphasizing the importance of administration timing. The observed differences across clinical strains emphasize the need for strain-specific evaluations and a deeper understanding of phage-antibiotic interactions to optimize therapy. Future research must focus on expanding phage diversity, refining protocols, and clinically validating sequential strategies to enhance PAC efficacy.

microbiology↗

bioRxiv2023

Glutamylation of Npm2 and Nap1 acidic disordered regions increases DNA charge mimicry to enhance chaperone efficiency

Histone chaperones-structurally diverse, non-catalytic proteins enriched with acidic intrinsically disordered regions (IDRs)-protect histones from spurious nucleic acid interactions and guide their deposition into and out of nucleosomes. Despite their conservation and ubiquity, the function of the chaperone acidic IDRs remains unclear. Here, we show that the Xenopus laevis Npm2 and Nap1 acidic IDRs are substrates for TTLL4 (Tubulin Tyrosine Ligase Like 4)-catalyzed post-translational glutamate-glutamylation. We demonstrate that, to bind, stabilize, and deposit histones into nucleosomes, chaperone acidic IDRs function as DNA mimetics. Our biochemical, computational, and biophysical studies reveal that glutamylation of these chaperone polyelectrolyte acidic stretches functions to enhance DNA electrostatic mimicry, promoting the binding and stabilization of H2A/H2B heterodimers and facilitating nucleosome assembly. This discovery provides insights into both the previously unclear function of the acidic IDRs and the regulatory role of post-translational modifications in chromatin dynamics.

biochemistry↗

bioRxiv2020

Transcriptomic and proteomic regulation through abundant, dynamic, and independent arginine methylation by Type I and Type II PRMTs

Arginine methylation is essential for both cellular viability and development and is also dysregulated in cancer. PRMTs catalyze the post translational monomethylation (Rme1/MMA, catalyzed by Type I-III), asymmetric (Rme2a/ADMA, Type I enzymes)-, or symmetric (Rme2s/SDMA, Type II enzymes) dimethylation of arginine. Despite many studies, a thorough integration of PRMT enzyme substrate determination and proteomic and transcriptomic consequences of inhibiting Type I and II PRMTs is lacking. To characterize cellular substrates for Type I (Rme2a) and Type II (Rme2s) PRMTs, human A549 lung adenocarcinoma cells were treated with either Type I (MS023) or Type II (GSK591) inhibitors. Using total proteome hydrolysis, we developed a new mass spectrometry approach to analyze total arginine and lysine content. We showed that Rme1 was a minor population ([~]0.1% of total arginine), Rme2a was highly abundant ([~]1.1%), and Rme2s was intermediate ([~]0.4%). While Rme2s was mostly eliminated by GSK591 treatment, total Rme1 and Rme2a were more resistant to perturbation. To quantitatively characterize substrate preferences of the major enzymes PRMT1, PRMT4(CARM1), and PRMT5, we used oriented peptide array libraries (OPAL) in methyltransferase assays. We demonstrated that while PRMT5 tolerates aspartic acid residues in the substrate, PRMT1 does not. Importantly, PRMT4 methylated previously uncharacterized hydrophobic motifs. To integrate our studies, we performed PTMScan on PRMT-inhibited A549 cells and enriched for methylated arginine containing tryptic peptides. For detection of highly charged peptides, a method to analyze the samples using electron transfer dissociation was developed. Proteomic analysis revealed distinct methylated species enriched in nuclear function, RNA-binding, intrinsically disordered domains, and liquid-liquid phase separation. Parallel studies with proteomics and RNA-Seq revealed distinct, but ontologically overlapping, consequences to PRMT inhibition. Overall, we demonstrate a wider PRMT substrate diversity and methylarginine functional consequence than previously shown.

molecular biology↗