Single molecule study of non-specific binding kinetics of LacI in mammalian cells

2015 ◽  
Vol 184 ◽  
pp. 393-400 ◽  
Author(s):  
Laura Caccianini ◽  
Davide Normanno ◽  
Ignacio Izeddin ◽  
Maxime Dahan
Keyword(s):  
Dna Binding ◽  
Single Molecule ◽  
Power Law ◽  
Mammalian Cells ◽  
Specific Binding ◽  
Lac Repressor ◽  
Striking Difference ◽  
Large Variability ◽  
U2os Cells ◽  
Kinetics Of

Many key cellular processes are controlled by the association of DNA-binding proteins (DBPs) to specific sites. The kinetics of the search process leading to the binding of DBPs to their target locus are largely determined by transient interactions with non-cognate DNA. Using single-molecule microscopy, we studied the dynamics and non-specific binding to DNA of the Lac repressor (LacI) in the environment of mammalian nuclei. We measured the distribution of the LacI–DNA binding times at non-cognate sites and determined the mean residence time to be τ1D = 182 ms. This non-specific interaction time, measured in the context of an exogenous system such as that of human U2OS cells, is remarkably different compared to that reported for the LacI in its native environment in E. coli (<5 ms). Such a striking difference (more than 30 fold) suggests that the genome, its organization, and the nuclear environment of mammalian cells play important roles on the dynamics of DBPs and their non-specific DNA interactions. Furthermore, we found that the distribution of off-target binding times follows a power law, similar to what was reported for TetR in U2OS cells. We argue that a possible molecular origin of such a power law distribution of residence times is the large variability of non-cognate sequences found in the mammalian nucleus by the diffusing DBPs.

scholarly journals Power-law behavior of transcription factor dynamics at the single-molecule level implies a continuum affinity model

2021 ◽  
Author(s):  
David A Garcia ◽  
Gregory Fettweis ◽  
Diego M Presman ◽  
Ville Paakinaho ◽  
Christopher Jarzynski ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Single Molecule ◽  
Power Law ◽  
Dwell Time ◽  
Specific Binding ◽  
Power Law Distribution ◽  
Single Molecule Level ◽  
Binding Behavior ◽  
Chromatin Template ◽  
Nuclear Domains

Abstract Single-molecule tracking (SMT) allows the study of transcription factor (TF) dynamics in the nucleus, giving important information regarding the diffusion and binding behavior of these proteins in the nuclear environment. Dwell time distributions obtained by SMT for most TFs appear to follow bi-exponential behavior. This has been ascribed to two discrete populations of TFs—one non-specifically bound to chromatin and another specifically bound to target sites, as implied by decades of biochemical studies. However, emerging studies suggest alternate models for dwell-time distributions, indicating the existence of more than two populations of TFs (multi-exponential distribution), or even the absence of discrete states altogether (power-law distribution). Here, we present an analytical pipeline to evaluate which model best explains SMT data. We find that a broad spectrum of TFs (including glucocorticoid receptor, oestrogen receptor, FOXA1, CTCF) follow a power-law distribution of dwell-times, blurring the temporal line between non-specific and specific binding, suggesting that productive binding may involve longer binding events than previously believed. From these observations, we propose a continuum of affinities model to explain TF dynamics, that is consistent with complex interactions of TFs with multiple nuclear domains as well as binding and searching on the chromatin template.

scholarly journals Power-law behaviour of transcription factor dynamics at the single-molecule level implies a continuum affinity model

2019 ◽  
Author(s):  
David A. Garcia ◽  
Gregory Fettweis ◽  
Diego M. Presman ◽  
Ville Paakinaho ◽  
Christopher Jarzynski ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Single Molecule ◽  
Power Law ◽  
Specific Binding ◽  
Power Law Distribution ◽  
Single Molecule Level ◽  
Complex Interactions ◽  
Chromatin Template ◽  
Nuclear Domains

ABSTRACTSingle-molecule tracking (SMT) allows the study of transcription factor (TF) dynamics in the nucleus, giving important information regarding the search and binding behaviour of these proteins in the nuclear environment. Dwell time distributions for most TFs have been described by SMT to follow bi-exponential behaviour. This is consistent with the existence of two discrete populations bound to chromatin in vivo, one non-specifically bound to chromatin (i.e. searching mode) and another specifically bound to target sites, as originally defined by decades of biochemical studies. However, alternative models have started to emerge, from multiple exponential components to power-law distributions. Here, we present an analytical pipeline with an unbiased model selection approach based on different statistical metrics to determine the model that best explains SMT data. We found that a broad spectrum of TFs (including glucocorticoid receptor, oestrogen receptor, FOXA1, CTCF) follow a power-law distribution, blurring the temporal line between non-specific and specific binding, and suggesting that productive binding may involve longer binding events than previously thought. We propose a continuum of affinities model to explain the experimental data, consistent with the movement of TFs through complex interactions with multiple nuclear domains as well as binding and searching on the chromatin template.

scholarly journals Mitotic chromosome binding predicts transcription factor properties in interphase

2018 ◽  
Author(s):  
Mahé Raccaud ◽  
Andrea B. Alber ◽  
Elias T. Friman ◽  
Harsha Agarwal ◽  
Cédric Deluz ◽  
...  
Keyword(s):  
Dna Binding ◽  
Single Molecule ◽  
Mitotic Chromosome ◽  
Specific Binding ◽  
Site Occupancy ◽  
Chromatin Accessibility ◽  
Live Cells ◽  
Specific Binding Sites ◽  
Genome Wide ◽  
Chromosome Binding

SummaryMammalian transcription factors (TFs) differ broadly in their nuclear mobility and sequence-specific/non-specific DNA binding affinity. How these properties affect the ability of TFs to occupy their specific binding sites in the genome and modify the epigenetic landscape is unclear. Here we combined live cell quantitative measurements of mitotic chromosome binding (MCB) of 502 TFs, measurements of TF mobility by fluorescence recovery after photobleaching, single molecule imaging of DNA binding in live cells, and genome-wide mapping of TF binding and chromatin accessibility. MCB scaled with interphase properties such as association with DNA-rich compartments, mobility, as well as large differences in genome-wide specific site occupancy that correlated with TF impact on chromatin accessibility. As MCB is largely mediated by electrostatic, non-specific TF-DNA interactions, our data suggests that non-specific DNA binding of TFs enhances their search for specific sites and thereby their impact on the accessible chromatin landscape.

scholarly journals Functional instability allows access to DNA in longer transcription Activator-Like effector (TALE) arrays

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Kathryn Geiger-Schuller ◽  
Jaba Mitra ◽  
Taekjip Ha ◽  
Doug Barrick
Keyword(s):  
Dna Binding ◽  
Single Molecule ◽  
Bound States ◽  
Fluorescence Analysis ◽  
Transcription Activator ◽  
External Energy ◽  
Functional Instability ◽  
Macromolecular Assembly ◽  
Kinetics Of ◽  
Superhelical Turn

Transcription activator-like effectors (TALEs) bind DNA through an array of tandem 34-residue repeats. How TALE repeat domains wrap around DNA, often extending more than 1.5 helical turns, without using external energy is not well understood. Here, we examine the kinetics of DNA binding of TALE arrays with varying numbers of identical repeats. Single molecule fluorescence analysis and deterministic modeling reveal conformational heterogeneity in both the free- and DNA-bound TALE arrays. Our findings, combined with previously identified partly folded states, indicate a TALE instability that is functionally important for DNA binding. For TALEs forming less than one superhelical turn around DNA, partly folded states inhibit DNA binding. In contrast, for TALEs forming more than one turn, partly folded states facilitate DNA binding, demonstrating a mode of ‘functional instability’ that facilitates macromolecular assembly. Increasing repeat number slows down interconversion between the various DNA-free and DNA-bound states.

scholarly journals Guided nuclear exploration increases CTCF target search efficiency

2018 ◽  
Author(s):  
Anders S. Hansen ◽  
Assaf Amitai ◽  
Claudia Cattoglio ◽  
Robert Tjian ◽  
Xavier Darzacq
Keyword(s):  
Dna Binding ◽  
Single Molecule ◽  
Mammalian Cells ◽  
Rna Binding ◽  
Target Search ◽  
Single Molecule Tracking ◽  
Search Mechanism ◽  
Binding Factor ◽  
Target Sites ◽  
Mammalian Genomes

Mammalian genomes are enormous. For a DNA-binding protein, this means that the number of non-specific, off-target sites vastly exceeds the number of specific, cognate sites. How mammalian DNA-binding proteins overcome this challenge to efficiently locate their target sites is not known. Here through live-cell single-molecule tracking, we show that CCCTC-binding factor, CTCF, is repeatedly trapped in small zones in the nucleus in a manner that is largely dependent on its RNA-binding region (RBR). Integrating theory, we devise a new model, Anisotropic Diffusion through transient Trapping in Zones (ADTZ), to explain this. Functionally, transient RBR-mediated trapping increases the efficiency of CTCF target search by ∼2.5 fold. Since the RBR-domain also mediates CTCF clustering, our results suggest a “guided” mechanism where CTCF clusters concentrate diffusing CTCF proteins near cognate binding sites, thus increasing the local ON-rate. We suggest that local “guiding” may represent a general target search mechanism in mammalian cells.

scholarly journals Direct substitution and assisted dissociation pathways for turning off transcription by a MerR-family metalloregulator

2012 ◽  
Vol 109 (38) ◽  
pp. 15121-15126 ◽  
Author(s):  
Chandra P. Joshi ◽  
Debashis Panda ◽  
Danya J. Martell ◽  
Nesha May Andoy ◽  
Tai-Yen Chen ◽  
...  
Keyword(s):  
Dna Binding ◽  
Single Molecule ◽  
Dna Sequences ◽  
Metal Binding ◽  
Metal Resistance ◽  
Binding Modes ◽  
Dynamic Interactions ◽  
Single Molecule Fret ◽  
Waste Energy ◽  
Kinetics Of

Metalloregulators regulate transcription in response to metal ions. Many studies have provided insights into how transcription is activated upon metal binding by MerR-family metalloregulators. In contrast, how transcription is turned off after activation is unclear. Turning off transcription promptly is important, however, as the cells would not want to continue expressing metal resistance genes and thus waste energy after metal stress is relieved. Using single-molecule FRET measurements we studied the dynamic interactions of the copper efflux regulator (CueR), a Cu+-responsive MerR-family metalloregulator, with DNA. Besides quantifying its DNA binding and unbinding kinetics, we discovered that CueR spontaneously flips its binding orientation at the recognition site. CueR also has two different binding modes, corresponding to interactions with specific and nonspecific DNA sequences, which would facilitate recognition localization. Most strikingly, a CueR molecule coming from solution can directly substitute for a DNA-bound CueR or assist the dissociation of the incumbent CueR, both of which are unique examples for any DNA-binding protein. The kinetics of the direct protein substitution and assisted dissociation reactions indicate that these two unique processes can provide efficient pathways to replace a DNA-bound holo-CueR with apo-CueR, thus turning off transcription promptly and facilely.

TMCC3 localizes at the three-way junctions for the proper tubular network of the endoplasmic reticulum

2019 ◽  
Vol 476 (21) ◽  
pp. 3241-3260
Author(s):  
Sindhu Wisesa ◽  
Yasunori Yamamoto ◽  
Toshiaki Sakisaka
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Membrane Protein ◽  
Mammalian Cells ◽  
Coiled Coil ◽  
Transmembrane Domains ◽  
Domain Family ◽  
Coiled Coil Domain ◽  
U2os Cells ◽  
Er Membrane

The tubular network of the endoplasmic reticulum (ER) is formed by connecting ER tubules through three-way junctions. Two classes of the conserved ER membrane proteins, atlastins and lunapark, have been shown to reside at the three-way junctions so far and be involved in the generation and stabilization of the three-way junctions. In this study, we report TMCC3 (transmembrane and coiled-coil domain family 3), a member of the TEX28 family, as another ER membrane protein that resides at the three-way junctions in mammalian cells. When the TEX28 family members were transfected into U2OS cells, TMCC3 specifically localized at the three-way junctions in the peripheral ER. TMCC3 bound to atlastins through the C-terminal transmembrane domains. A TMCC3 mutant lacking the N-terminal coiled-coil domain abolished localization to the three-way junctions, suggesting that TMCC3 localized independently of binding to atlastins. TMCC3 knockdown caused a decrease in the number of three-way junctions and expansion of ER sheets, leading to a reduction of the tubular ER network in U2OS cells. The TMCC3 knockdown phenotype was partially rescued by the overexpression of atlastin-2, suggesting that TMCC3 knockdown would decrease the activity of atlastins. These results indicate that TMCC3 localizes at the three-way junctions for the proper tubular ER network.

Single-Molecule Imaging of Active Mitochondrial Nitroreductases using a Photo-Crosslinking Fluorescent Sensor

2019 ◽  
Author(s):  
Zacharias Thiel ◽  
Pablo Rivera-Fuentes
Keyword(s):  
Subcellular Localization ◽  
Fluorescent Probe ◽  
Single Molecule ◽  
Mammalian Cells ◽  
Fluorescent Sensor ◽  
Biological Functions ◽  
Localization Microscopy ◽  
Drug Activation ◽  
Nitroreductase Activity ◽  
Single Molecule Localization Microscopy

Many biomacromolecules are known to cluster in microdomains with specific subcellular localization. In the case of enzymes, this clustering greatly defines their biological functions. Nitroreductases are enzymes capable of reducing nitro groups to amines and play a role in detoxification and pro-drug activation. Although nitroreductase activity has been detected in mammalian cells, the subcellular localization of this activity remains incompletely characterized. Here, we report a fluorescent probe that enables super-resolved imaging of pools of nitroreductase activity within mitochondria. This probe is activated sequentially by nitroreductases and light to give a photo-crosslinked adduct of active enzymes. In combination with a general photoactivatable marker of mitochondria, we performed two-color, threedimensional, single-molecule localization microscopy. These experiments allowed us to image the sub-mitochondrial organization of microdomains of nitroreductase activity.<br>

Single-Molecule Imaging of Active Mitochondrial Nitroreductases using a Photo-Crosslinking Fluorescent Sensor

2019 ◽  
Author(s):  
Zacharias Thiel ◽  
Pablo Rivera-Fuentes
Keyword(s):  
Subcellular Localization ◽  
Fluorescent Probe ◽  
Single Molecule ◽  
Mammalian Cells ◽  
Fluorescent Sensor ◽  
Biological Functions ◽  
Localization Microscopy ◽  
Drug Activation ◽  
Nitroreductase Activity ◽  
Single Molecule Localization Microscopy

Many biomacromolecules are known to cluster in microdomains with specific subcellular localization. In the case of enzymes, this clustering greatly defines their biological functions. Nitroreductases are enzymes capable of reducing nitro groups to amines and play a role in detoxification and pro-drug activation. Although nitroreductase activity has been detected in mammalian cells, the subcellular localization of this activity remains incompletely characterized. Here, we report a fluorescent probe that enables super-resolved imaging of pools of nitroreductase activity within mitochondria. This probe is activated sequentially by nitroreductases and light to give a photo-crosslinked adduct of active enzymes. In combination with a general photoactivatable marker of mitochondria, we performed two-color, threedimensional, single-molecule localization microscopy. These experiments allowed us to image the sub-mitochondrial organization of microdomains of nitroreductase activity.<br>

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