Single-molecule live imaging of subunit interactions and exchange within cellular regulatory complexes.

Cells are built from vast networks of interdependent molecular interactions. Here, we combine proximity-assisted photoactivation (PAPA) with automated fast single-molecule tracking (fSMT) to probe subunit interactions within endogenous protein complexes in live human cells. PAPA-fSMT revealed that the inactive positive transcription elongation factor b (P-TEFb):7SK ribonucleoprotein complex is predominantly mobile, not tethered to chromatin, and detected interaction of specific heterogeneous nuclear ribonucleoproteins (hnRNPs) with the 7SK complex.

Bis(trifluoromethyl)carborhodamines: Highly Fluorogenic, Far-Red to Near-Infrared Dyes for Live Cell Fluorescence Microscopy, Activity-Based Sensing, and Single-Molecule Microscopy.

Synthetic fluorophores built on a classic rhodamine scaffold are essential for modern microscopy. An attractive feature of synthetic fluorophores is their potential to access long-wavelength excitation and emission profiles (>650 nm) that are difficult to achieve through genetically encoded methods like fluorescent proteins. Here, we present a new strategy to achieve excitation and emission above 650 nm: bis(trifluoromethyl)carborhodamine dyes, or BF dyes.

Assembly and Dynamics of Transcription Initiation Complexes.

Gene expression is essential for life and development, allowing the cell to modulate mRNA production in response to intrinsic and extracellular cues. Initiation of gene transcription requires a highly regulated molecular process to assemble multisubunit complexes into the preinitiation complex (PIC). Attempts to visualize these processes have been driven largely by electron microscopy, with near atomic-level resolution producing static snapshots complemented by low-resolution fluorescence cell imaging.

Automated live-cell single-molecule tracking in enteroid monolayers reveals transcription factor dynamics probing lineage-determining function.

Lineage transcription factors (TFs) provide one regulatory level of differentiation crucial for the generation and maintenance of healthy tissues. To probe TF function by measuring their dynamics during adult intestinal homeostasis, we established HILO-illumination-based live-cell single-molecule tracking (SMT) in mouse small intestinal enteroid monolayers recapitulating tissue differentiation hierarchies in vitro. To increase the throughput, capture cellular features, and correlate morphological characteristics with diffusion parameters, we developed an automated imaging and analysis pipeline, broadly applicable to two-dimensional culture systems.

Thermodynamic architecture and conformational plasticity of GPCRs.

G-protein-coupled receptors (GPCRs) are ubiquitous integral membrane proteins involved in diverse cellular signaling processes. Here, we carry out a large-scale ensemble thermodynamic study of 45 ligand-free GPCRs employing a structure-based statistical mechanical framework. We find that multiple partially structured states co-exist in the GPCR native ensemble, with the TM helices 1, 6 and 7 displaying varied folding status, and shaping the conformational landscape.

Probing patterning in microbial consortia with a cellular automaton for spatial organisation.

Microbial consortia exhibit spatial patterning across diverse environments. Since probing the self-organization of natural microbial communities is limited by their inherent complexity, synthetic models have emerged as attractive alternatives. In this study, we develop novel frameworks of bacterial communication and explore the emergent spatiotemporal organization of microbes.

pPerturb: A Server for Predicting Long-Distance Energetic Couplings and Mutation-Induced Stability Changes in Proteins via Perturbations.

The strength of intraprotein interactions or contact network is one of the dominant factors determining the thermodynamic stabilities of proteins. The nature and the extent of connectivity of this network also play a role in allosteric signal propagation characteristics upon ligand binding to a protein domain. Here, we develop a server for rapid quantification of the strength of an interaction network by employing an experimentally consistent perturbation approach previously validated against a large data set of 375 mutations in 19 different proteins.