Biology subjects

Kros, A.

Publications and source records attributed to Kros, A..

5 recordsLinked to original sources

bioRxiv2026

A single-nucleotide change in the Kozak sequence enhances protein expression

In vitro-transcribed messenger RNA (IVT mRNA) has emerged as a versatile protein expression platform with broad clinical potential. Current optimization strategies for IVT mRNA focus on untranslated regions (UTRs), mRNA stability, and codon usage, often guided by massively parallel screening and machine learning approaches. In contrast, the Kozak sequence, a key determinant of translation initiation, is often inconsistently incorporated into synthetic 5' UTR design, and its contribution to translation efficiency remains poorly defined. Here, we systematically varied the Kozak sequence across diverse UTR contexts and performed combinatorial optimization using synthetic, established, and viral UTRs to identify design principles for enhanced translation. We show that a single-nucleotide deviation from the consensus Kozak sequence consistently enhances protein expression across UTR contexts and coding sequences. This effect is conserved across in vitro and in vivo models, highlighting the generalizability of the optimized Kozak sequence. These findings redefine the role of the Kozak sequence in synthetic mRNA design and demonstrate its substantial contribution to translation efficiency when optimized, enabling improved mRNA-based therapeutics.

bioengineering↗

bioRxiv2026

A narrow thermodynamic design window governs selective membrane permeabilization and antiviral activity of amphipathic peptides

Designing molecules that selectively target therapeutically relevant membranes, such as viral envelopes, while sparing host cells is challenging: these membranes closely resemble host bilayers, so selectivity must exploit subtle lipid composition and curvature differences and demands precise tuning of affinity and hydrophobicity, yet curated sequence-specificity data are scarce. Here we show that selective membrane permeabilization and membrane-selective activity of amphipathic peptides are governed by a narrow thermodynamic design window defined by membrane curvature affinity and molecular hydrophobicity. Using a physics-driven generative workflow combining evolutionary molecular dynamics and a transformer predictor (PMIpred), we systematically explored and thermodynamically mapped peptide sequence space de novo without reliance on natural templates or experimental training data. Across four design generations we synthesized and experimentally characterized 43 peptides. Mapping functional activity onto a low-dimensional free-energy landscape reveals a confined thermodynamic "sweet spot" separating weak membrane binding from excessive hydrophobic association and cytotoxicity. Peptides operating within this regime efficiently permeabilize model membranes while maintaining low cellular toxicity. Antiviral activity against Zika virus and HIV-1 emerges in the same region but depends sensitively on membrane lipid composition. Quantitative thermodynamic design rules emerge for membrane-active peptides, illustrating how low-dimensional free-energy landscapes can guide the engineering of selective interactions at soft-matter interfaces.

biophysics↗

bioRxiv2026

The missing link between biomolecular condensates and amyloid fibrils

The traditional view of protein self-assembly posits a binary choice between phase separation into fluid condensates and nucleation into crystalline amyloid fibers. However, this framework is incomplete. Experiments show that liquid condensates are non-equilibrium systems that mature into solid-like structures mediated by amphiphilic prion-like domains (PLDs). Being spatially organized yet dynamic, lyotropic phases represent an intermediate regime between these states. Using physics-based de novo protein design (Evo-MD), we identify a vast amphiphilic motif space encoding fluid lyotropic phases (e.g., micelles and bicelles). TEM, CD, and AlphaFold predictions confirm that these motifs also assemble into amyloid-based hydrogels as thermodynamic endpoints. Notably, the molecular grammar of lyotropic motifs overlaps strongly with that of PLDs and LARKS. Thus, while PLDs likely evolved to stabilize condensates through transient interactions near criticality, our results show that these same amphiphilic forces inherently encode lyotropic structuring and subsequent amyloid formation - linking functional condensation with pathological aggregation.

biophysics↗

bioRxiv2022

DNA uptake by cell wall-deficient bacteria reveals a putative ancient macromolecule uptake mechanism

Horizontal gene transfer in bacteria is widely believed to occur via three main mechanisms: conjugation, transduction and transformation. These mechanisms facilitate the passage of DNA across the protective cell wall using sophisticated machinery. We present here a new mechanism of DNA uptake that is independent of canonical DNA uptake machineries and is used by bacteria that live without a cell wall. We show that the cell wall-deficient bacteria engulf extracellular material, whereby intracellular vesicles are formed, and DNA is internalized. This mechanism is not specific to DNA, and allows uptake of other macromolecules and even 125 nm lipid nanoparticles (LNPs). Uptake was prevented by molecules known to inhibit eukaryotic endocytosis, suggesting this to be an energy-dependent process. Given that cell wall-deficient bacteria are considered a model for early life forms, our work provides a possible mechanism for primordial cells to acquire new genetic material or food before invention of the bacterial cell wall.

microbiology↗

bioRxiv2021

Generating heterokaryotic cells via bacterial cell-cell fusion

Cell-cell fusion is fundamentally important for tissue repair, virus transmission, and genetic recombination, among other functions. Fusion has been mainly studied in eukaryotic cells and lipid vesicles, while cell-cell fusion in bacteria is less well characterized, due to the cell wall acting as a fusion-limiting barrier. Here we use cell wall-deficient bacteria to investigate the dynamics of cell fusion in bacteria that replicate without their cell wall. Stable, replicating cells containing differently labeled chromosomes were successfully obtained from fusion. We find that the rate of cell-cell fusion depends on the fluidity of cell membranes. Furthermore, we show that not only the efficiency but also the specificity of cell-cell fusion can be controlled via a pair of synthetic membrane-associated lipopeptides. Our results provide a molecular handle to understand and control cell-cell fusion to generate heterokaryotic cells, which was an important step in the evolution of protocells and of increasing importance for the design of synthetic cells.

microbiology↗