Engineered fast-dissociating antibody fragments for multiplexed super-resolution microscopy

IntAct: A nondisruptive internal tagging strategy to study the organization and function of actin isoforms

Mammals have 6 highly conserved actin isoforms with nonredundant biological functions. The molecular basis of isoform specificity, however, remains elusive due to a lack of tools. Here, we describe the development of IntAct, an internal tagging strategy to study actin isoforms in fixed and living cells. We identified a residue pair in β-actin that permits tag integration and used knock-in cell lines to demonstrate that IntAct β-actin expression and filament incorporation is indistinguishable from wild type. Furthermore, IntAct β-actin remains associated with common actin-binding proteins (ABPs) and can be targeted in living cells. We demonstrate the usability of IntAct for actin isoform investigations by showing that actin isoform-specific distribution is maintained in human cells. Lastly, we observed a variant-dependent incorporation of tagged actin variants into yeast actin patches, cables, and cytokinetic rings demonstrating cross species applicability. Together, our data indicate that IntAct is a versatile tool to study actin isoform localization, dynamics, and molecular interactions.

Single-Molecule Localization Microscopy Using Time-Lapse Imaging of Single-Antibody Labeling

In single-molecule localization microscopy (SMLM), immunofluorescence (IF) staining affects the quality of the reconstructed superresolution images. However, optimizing IF staining remains challenging because IF staining is a one-step, irreversible process. Sample labeling through reversible binding presents an alternative strategy, but such techniques require significant technological advancements to enhance the dissociation of labels without sacrificing their binding specificity. In this article, we introduce time-lapse imaging of single-antibody labeling. Our versatile technique utilizes commercially available dye-conjugated antibodies. The method controls the antibody concentrations to capture single-antibody labeling of subcellular targets, thereby achieving SMLM through the labeling process. We further demonstrate dual-color single-antibody labeling to enhance the sample labeling density. The new approach allows the evaluation of antibody binding at the single-antibody level and within the cellular environment. This comprehensive guide offers step-by-step instructions for time-lapse imaging of single-antibody labeling experiments and enables the application of the single-antibody labeling technique to a wide range of targets. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Sample preparation for single-antibody labeling Basic Protocol 2: Data acquisition for single-molecule localization microscopy Alternate Protocol: Dual-color single-antibody labeling using OptoSplit II equation Basic Protocol 3: Image analysis.

When Weak Is Strong: A Plea for Low-Affinity Binders for Optical Microscopy

The exploitation of low-affinity molecular interactions in protein labeling is an emerging topic in optical microscopy. Such non-covalent and low-affinity interactions can be realized with various concepts from chemistry and for different molecule classes, and lead to a constant renewal of fluorescence signals at target sites. Further benefits are a versatile use across microscopy methods, in 3D, live and many-target applications. In recent years, several classes of low-affinity labels were developed and a variety of powerful applications demonstrated. Still, this research field is underdeveloped, while the potential is huge.

Beyond DNA: new probes for PAINT super-resolution microscopy

In the last decade, point accumulation for imaging in nanoscale topography (PAINT) has emerged as a versatile tool for single-molecule localization microscopy (SMLM). Currently, DNA-PAINT is the most widely used, in which a transient stochastically binding DNA docking-imaging pair is used to reconstruct specific characteristics of biological or synthetic materials on a single-molecule level. Slowly, the need for PAINT probes that are not dependent on DNA has emerged. These probes can be based on (i) endogenous interactions, (ii) engineered binders, (iii) fusion proteins, or (iv) synthetic molecules and provide complementary applications for SMLM. Therefore, researchers have been expanding the PAINT toolbox with new probes. In this review, we provide an overview of the currently existing probes that go beyond DNA and their applications and challenges.

Superresolution Imaging with Single-Antibody Labeling

We present a versatile single-molecule localization microscopy technique utilizing time-lapse imaging of single-antibody labeling. By performing single-molecule imaging in the subminute time scale and tuning the antibody concentration to create sparse single-molecule binding, we captured antibody labeling of subcellular targets to generate superresolution images. Single-antibody labeling enabled dual-target superresolution imaging using dye-conjugated monoclonal and polyclonal antibodies. We further demonstrate a dual-color strategy to increase the sample labeling density. Single-antibody labeling paves a new way to evaluate antibody binding for superresolution imaging in the native cellular environment.