Biophysics HT Seminar 2

Talk 1:Single molecule insights into cellular mechanotransduction
Prof Sergi Garcia-Manyes, Single Molecule Mechanobiology Laboratory, Francis-Crick Institute & King’s College London (Biophysics)

Cellular mechanostransduction relies on the conversion of mechanical cues into chemical signals, which propagate from the focal adhesion hub through the cytoskeleton to ultimately reach the nucleus through the Nuclear Pore Complex (NPC), and switch on specific force-dependent transcriptional programmes. However, how cellular mechanotransduction is regulated by the nanomechanical properties of the underpinning force-bearing proteins remains largely unknown. Here we first used a newly developed single-molecule magnetic tweezers combined with UV-light to demonstrate that oxidation of a previously cryptic methionine in the talin mechanosensor impairs vinculin binding. When translating the single-molecule findings into the cellular context, we found a loss in talin/vinculin co-localisation at focal adhesions of NIH3T3 mouse fibroblasts when exposed to µM concentrations of H2O2 and a decrease in the nuclear localisation of the YAP transcription factor (TF). In this vein, how the nuclear shuttling of mechanosensitive TFs is regulated by their mechanical properties remains also unclear. By using a combination of single-molecule mechanics and single-cell optogenetics, we discovered that proteins with locally soft regions in the vicinity of the nuclear-localization sequence exhibit higher nuclear-import rates. Inspired by these findings, we designed a short and easy-to-express unstructured peptide tag that accelerates the nuclear-import rate of stiff protein cargos. Altogether, our cross-scale experiments provide a single molecule perspective onto cellular mechanotransduction.

Talk 2: See it to believe it: using microscopy to test the current model of F plasmid conjugation
Alfredas Bukys, Berks Group, Oxford Dept of Biochemistry

Conjugative plasmids, such as those related to the fertility factor (F), allow bacteria to horizontally transfer antibiotic resistance and/or virulence genes, granting the ability to convert commensal strains into pathogenic ones or generate multi-drug resistant strains. In gram-negative bacteria, conjugation is mediated by the Type IV secretion system. While much work has been done on biochemical characterisation of conjugation, less effort had been made to inspect the process via microscopy until recently. Here I use a fluorescent reporter-operator system to test the current model of conjugation, specifically whether F plasmids form a pre-initiation complex.