Lomakin, I. B. | bioRxiv Science

bioRxiv2025

Structures redefine the mechanism of action for tetracyclines

The tetracycline class of antibiotics is widely used for treating bacterial diseases including Lyme disease, anthrax, acne vulgaris, and pneumonia. Using a series of high-resolution cryo-electron microscopy (cryo-EM) structures, we show that tetracyclines can simultaneously target the mRNA decoding center and the nascent peptide exit tunnel (NPET) of the bacterial 70S ribosome. Among the tested tetracyclines, Doxycycline was unique in its ability to dimerize and bind the NPET at multiple locations. Structural comparison of Doxycycline, Minocycline, and Sarecycline bound to the Escherichia coli and Cutibacterium acnes 70S ribosome revealed species-specific differences affecting drug interaction and occupancy. Our results redefine the mechanism of action for tetracyclines and provide a structural basis for rational design of narrow spectrum tetracyclines to overcome the rising threat of antibiotic resistance.

microbiology↗

bioRxiv2024

Visualizing the translation landscape in human cells at high resolution

Obtaining comprehensive structural descriptions of macromolecules within their natural cellular context holds immense potential for understanding fundamental biology and improving health. Here, we present the landscape of protein synthesis inside human cells in unprecedented detail obtained using an approach which combines automated cryo-focused ion beam (FIB) milling and in situ single-particle cryo-electron microscopy (cryo-EM). With this in situ cryo-EM approach we resolved a 2.19 [A] consensus structure of the human 80S ribosome and unveiled its 21 distinct functional states, nearly all higher than 3 [A] resolution. In contrast to in vitro studies, we identified protein factors, including SERBP1, EDF1 and NAC/3, not enriched on purified ribosomes. Most strikingly, we observed that SERBP1 binds to the ribosome in almost all translating and non-translating states to bridge the 60S and 40S ribosomal subunits. These newly observed binding sites suggest that SERBP1 may serve an important regulatory role in translation. We also uncovered a detailed interface between adjacent translating ribosomes which can form the helical polysome structure. Finally, we resolved high-resolution structures from cells treated with homoharringtonine and cycloheximide, and identified numerous polyamines bound to the ribosome, including a spermidine that interacts with cycloheximide bound at the E site of the ribosome, underscoring the importance of high-resolution in situ studies in the complex native environment. Collectively, our work represents a significant advancement in detailed structural studies within cellular contexts.

molecular biology↗